LGMANS' 


HANDICRAFT  SERIES 


Ml 


TRODUCTION 

•HHHi 

G  SCIE 


J.  B,  COPPOCK 

AND 

G,  A,  LODGE 


MODERN  PRACTICE  IN  MINING.      By  Sir  R.  A.  S. 
REDMAYNE,  K.C.B.,  M.Sc.,  M.Inst.C.E.,  M.Inst.M.E., 
F.G.S.,  His  Majesty's  Chief  Inspector  of  Mines.     8vo. 
Vol.  I.      Coal,  its  Occurrence,  Value,  and  Methods  of 

Boring.     With  123  Illustrations  and  19  Sets  of  Tables. 

6s.  net. 
Vol.  II.     The  Sinking  of  Shafts.     With  172  Illustrations 

and  7  Sets  of  Tables,     js.  6d.  net. 
Vol.  III.      Methods  of  Working  Coal.     With  Folding 

Plan  and  other  Illustrations.     6*.  6d.  net. 
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Plans,    107    Illustrations,    and    21    Sets    of    Tables. 

6s.  6d.  net. 
Vol.  V.     Colliery  Machinery  and  its  Application. 

COAL,  AND  THE  PREVENTION  OF  EXPLOSIONS 
AND  FIRES  IN  MINES.  By  JOHN  HARGER,  M.Sc. 
(Victoria),  Ph.D.  (Heidelberg),  M.Inst.M.E.  8vo, 
35.  6d.  net. 

MINING.  An  Elementary  Treatise  on  the  Getting  of 
Minerals.  With  a  Geological  Map  of  the  British  Isles 
and  596  Diagrams  and  Illustrations.  By  ARNOLD 
LUPTON,  M.I.C.E.,  F.G.S.  Crown  8vo,  gs.  net. 

A  PRACTICAL  TREATISE  ON  MINE  SURVEYING. 
With  216  Diagrams.  By  ARNOLD  LUPTON,  M.I.C.E., 
F.G.S.  Medium  8vo,  12.?.  net.  . 

ENGINEER'S  VALUING  ASSISTANT:  being  a 
Practical  Treatise  on  the  Valuation  of  Collieries  and 
other  Mines,  with  Rules,  Formulae  and  Examples.  By 
H.  D.  HOSKOLD.  8vo,  75.  6d.  net. 

ELEMENTARY  CHEMISTRY  FOR  COAL-MINING 
STUDENTS.  By  L.  T.  O'SHEA,  M.Sc.,  Professor  of 
Applied  Chemistry  at  the  Sheffield  University.  With 
Diagrams.  Crown  8vo,  6s.  net. 

LONGMANS,  GREEN  AND  CO. 

LONDON,  NEW  YORK,  BOMBAY,  CALCUTTA,  AND  MADRAS 


LONGMANS'  TECHNICAL   HANDICRAFT  SERIES 


AN  INTRODUCTION 

TO 

MINING     SCIENCE 


LONGMANS'  TECHNICAL   HANDICRAFT  SERIES 


AN  INTRODUCTION 


TO 


MINING    SCIENCE 

A  THEORETICAL  AND  PRACTICAL  TEXTBOOK 
FOR  MINING  STUDENTS 


BY 
JOHN  B.  COPPOCK,  B.Sc.  (LOND.),  F.I.C.,  F.C.S, 

ASSOCIATE   OF   NOTTINGHAM    UNIVERSITY  COLLEGE  ; 

OF  THE    WEST    RIDING    EDUCATION    AUTHORITY  J 
AUTHOR   OF    "VOLUMETRIC  ANALYSIS";   "THE    SCIENCE   OF   COMMON    LIFE" 

AND 

G.  A.  LODGE,   M.lNST.M.E. 

LECTURER   ON    MINING   AND    MINE    SURVEYING   AT    HUDDERSFIELD    TECHNICAL 
COLLEGE    AND    BATLEY   TECHNICAL    SCHOOL 


WITH  DIAGRAMS 


LONGMANS,     GREEN     AND     CO. 
39    PATERNOSTER    ROW,     LONDON 

FOURTH  AVENUE  &  30TH  STREET,  NEW  YORK 
BOMBAY,  CALCUTTA,  AND  MADRAS 

1915 

All  rights  reserved 


RESPECTFULLY    DEDICATED 


EDWIN  TALBOT,  ESQ.,  J.P.,  C.C. 

CHAIRMAN   OF  THE   HIGHER   EDUCATION   COMMITTEE  OF 
THE   WEST   RIDING  OF   YORKSHIRE 


IN    RECOGNITION    OF    THE    REFORM    AND    ADVANCE 
ACCOMPLISHED    IN    CONNECTION    WITH    MINING    EDUCATION 


333946 


PREFACE. 

i.  THE  SCIENCE  SECTION. 

THE  education  of  the  miner  in  the  scientific  and 
technical  aspects  of  his  work  is  receiving  attention 
from  National  and  Local  Education  Authorities, 
from  the  employer,  and  what  is  more  promising- 
still,  from  the  miner  himself.  This  has  resulted 
in  throwing  into  the  melting-pot  old  schemes  of 
instruction,  in  the  skimming  oft  the  dross,  and  the 
introduction  of  the  experimental  method  into  class 
work.  The  latter  it  is  felt  will  sustain  interest ;  it  is 
sure  to  develop  intelligence  and  correct  ideas. 

The  teaching  of  science  to  the  miner,  adult  or 
adolescent,  and  to  the  rank  and  file  of  any  industry, 
has  got  to  be  considerably  changed  if  it  is  to  grow  in 
popularity.  The  failure  in  teaching  to  connect  the 
fundamental  facts  of  science  with  the  experience  of 
daily  life,  and  to  phrase  our  language  in  the  words 
of  the  students'  vocabulary,  are  great  weaknesses  in 
our  methods.  The  science  side  of  this  book  there- 
fore attempts  to  use  the  experience  of  a  student  as 
a  means  of  developing  a  scientific  fact,  just  as  the 
moral  educationist  uses  the  experience  of  daily  life 
in  his  object  lessons  to  the  young. 

Questions  have  been  added  to  each  Chapter  in  this 
section ;  the  majority  have  been  designed  so  as  to 
expand  the  teaching  of  the  text  at  the  same  time  as 
they  use  its  information. 

JOHN  B.  COPPOCK. 


viii  Preface. 

2.  THE  PRACTICAL  APPLICATION  TO  MINING. 

The  question  of  safety  in  mines  is  of  the  greatest 
importance,  and  believing  that  increased  safety  will 
be  best  attained  by  increasing  the  intelligence  of  the 
miner,  the  practical  part  is  mostly  confined  to  a  simple 
description  of  things  which  are  important  from  the 
safety  point  of  view. 

Extracts  from  the  Coal  Mines 'Act  and  Regulations 
and  from  Inspectors'  Reports  on  accidents  in  mines  are 
freely  given  in  the  hope  that  lessons  will  be  learnt 
therefrom  and  accidents  decrease.  If  the  student  can 
be  made  to  realize  that  great  things  are  built  up  of 
little  ones,  and  that  only  close  observation  and  under- 
standing of  details  will  lead  to  the  understanding  of 
the  whole,  much  will  be  accomplished. 

GEO.  A.  LODGE. 

3.  ACKNOWLEDGMENTS. 

The  Authors  have  to  acknowledge  their  indebted- 
ness to  Mr.  F.  N.  Cook  and  Mr.  L.  K.  Hindmarsh 
of  the  West  Riding  Education  Authority,  for  their 
valuable  help  in  revision.  They  have  further  to 
thank  Miss  Coppock  for  original  drawings  and  Messrs. 
Longmans,  Green  and  Co.  for  permission  to  use  many 
blocks  belonging  to  Newth's  and  Furneaux's  works  on 
Chemistry. 

J.   B.   C. 
G.  A.   L. 


CONTENTS. 


I.  Combustible  and  Incombustible  Substances     .         .          i 
Practical  Application  to  Mining. 

II.  The  Air:  its  Constituents  and  its  Actions          .         .        16 
Practical  Application  to  Mining. 

III.  Air  Currents  and  How  they  are  Caused  ...       44 
Practical  Application  to  Mining. 

IV.  The  Increase  in  Size  of  Substances  by  Heat,  and  its 

Applications    .......       67 

Practical  Application  to  Mining. 

V.  The  Principle  of  the  Safety  Lamp  ...       83 

Practical  Application  to  Mining. 

VI.  The  Mine  Gases  Known  as  Damps         .         .         .     105 
Practical  Application  to  Mining. 

VII.  Substances  which,  mixed  with  Air,  form  Explosive 

Mixtures 128 

Practical  Application  to  Mining. 

VIII.  Flames  :  their  Shapes  and  Parts      .         .         .         .143 
IX.  Ways  of  Producing  Heat  and  Light         .         .         .     157 

X.  The  Inflammability  of  Substances   .         .         .         .167 
Practical  Application  to  Mining. 

XI.  Substances  Containing  Fixed  Oxygen       .         .  179 

Practical  Application  to  Mining. 

XII.  Diffusion,  or  the  Movement  of  Gas  Particles   .         .      192 

XIII.  Substances  and  their  Changes         ....     200 

Practical  Application  to  Mining. 

XIV.  Coal :  its  Nature  and  Origin 212 

Practical  Application  to  Mining. 


Index 


227 


NOTE  TO  STUDENT. 

CERTAIN  of  the  Experiments  in  this  book  have  a  C 
placed  to  the  right  hand  of  the  instructions  ;  it  stands 
for  Caution.  There  is  no  danger  in  carrying  out 
these  experiments  if  the  instructions  are  followed  and 
thoughtfulness  exercised. 


CHAPTER  I. 
COMBUSTIBLE  AND  INCOMBUSTIBLE  SUBSTANCES. 

A  YOUNG  child  acts  on  the  idea  that  all  things  thrown  on 
the  fire  will  burn,  and  so  he  is  inclined  to  throw  on  to  it  not 
only  paper,  which  gives  the  looked-for  result,  but  stones  as 
well.  As  the  child  develops  he  begins  to  realize  that  stones 
will  not  burn,  and  so  there  grows  in  his  mind  the  idea  that 
there  are  two  kinds  of  things — those  which  will  and  those 
which  will  not  burn.  These  are  most  important  conclusions, 
they  finally 'become  well  established  in  the  child's  mind  by 
his  experience ;  and  when  later  on  in  life  the  power  of  re- 
flecting on  facts  is  added  to  his  mental  equipment,  he  finds 
that  the  things  which  burn  come  from  either  the  animal 
or  plant  world,  and  the  things  which  do  not  burn  come  from 
other  sources.  The  child  also  begins  to  see  that  things 
burn  with  different  degrees  of  quickness  and  more  or  less 
flame  :  paper  quickly,  but  cardboard  slowly.  A  leaf  of  a  tree 
burns  quickly  or  slowly  according  to  its  dryness,  often  with 
much  flare,  and  gradually  he  realizes  that  when  there  is 
quick  burning  there  is  more  flame  than  in  slow  burning. 

Experience. 

Most  people  have  noticed  the  quickness  of  combustion  of  the 
floral  decorations  of  a  house,  e.g.  holly,  when  taken  down  after 
Christmas  ;  the  rapidity  and  vigour  of  the  burning  suggests  that 
of  a  piece  of  celluloid.  A  very  dry  leaf  burns  violently,  and  dry 
orange-peel  gives  little  explosions  with  a  big  blaze.  It  is  well 
known  that  dry  holly  is  more  dangerous  than  freshly  gathered 
holly  ;  in  the  latter  case  the  combustion  is  slow  and  can  be 
easily  kept  under  control,  whereas  with  the  dried  holly  there  is  a 
"  flare  up  "  at  once. 

A  well-known  piece  of  experience  may  be  repeated  to 
bring  out  some  of  the  foregoing  points. 

I 


2'  •*    '      .  ///  •  Jntroihtotion  to  Mining  Science. 

Experiment, 

Strike  a  match  and  carefully  notice  the  difference  between  the 
quickness  in  the  burning  of  the  head  and  stick. 

There  is  no  doubt  that  the  stick  undergoes  a  slower  com- 
bustion than  the  head,  and  that  the  rapidity  of  combustion 
of  the  head  is  more  like  a  small  explosion.  In  fact,  some- 
times when  a  match  is  struck  the  head  bursts  very  quickly, 
or  suddenly — it  is  an  example  of  a  real  but  a  small  explosion. 
Most  boys  know  that  a  "squib  "  after  lighting  goes  off  very 
gently  for  a  few  seconds  and  then  finishes  with  a  bang ;  the 
bang  is  due  to  the  sudden  heating  of  a  bit  of  tightly  packed 
powder  at  the  end  of  the  squib.  The  end  all  at  once 
ignites,  and  a  small  explosion  is  the  result ;  by  all  at  once  is 
meant  that  the  action  instead  of  taking  a  second  or  two  is  over 
in  a  thousandth  part  of  a  second.  Instantaneous  combustion 
is  the  very  essence  of  an  explosion. 

Experience, 

A  lighted  cigarette,  cigar,  or  pipe  of  tobacco  affords  an  illus- 
tration of  slow  combustion,  particularly  so  when  it  is  away  from 
the  mouth.  The  combustion  is  made  quicker  by  the  action  of 
"  drawing  through  "  the  burning  tobacco. 

The  last  piece  of  familiar  experience  should  be  carefully 
thought  of,  so  as  to  understand  how  the  tobacco  in  each 
case  keeps  burning.  Air  is  drawn  through  the  burning  mass 
of  tobacco  ;  when  the  air  is  drawn  through  the  surface  of  the 
tobacco  glows  with  fire,  and  on  ceasing  to  draw  the  glow 
dies  down  ;  if  left  too  long  the  burning  ceases.  The  fore- 
going is  one  of  the  simplest  pieces  of  experience  which 
points  out  very  definitely  that  the  air  is  in  some  way  con- 
nected with  the  burning  of  a  substance. 

Slow  and  Quick  Combustion, 

Combustion  in  many  cases  may  go  on  extremely  slowly 
and  without  the  production  of  flame,  and  there  is  nothing 
to  show  there  is  combustion,  except  a  higher  temperature 
than  the  air,  e.g.  the  heat  of  our  body  is  produced  by  the 
glow  combustion  of  our  food  after  it  has  been  digested  and 


Combustible  and  Incombustible  Substances.          3 

found  its  way  into  the  stream  of  blood.  The  rusting  of 
iron  is  combustion  but  much  slower  than  the  foregoing, 
nevertheless  heat  is  produced. 

Experience. 

Iron  railings  or  other  iron  structures,  if  left  unpainted,  will 
rust  ;  this  leads  to  the  structure  gradually  wearing  away  by  the 
falling  off  of  thin  layers  of  rotted  or  rusted-iron. 

A  man  of  science  would  say  that  rusting  is  a  process  of 
combustion  in  which  the  substance  rusting  and  the  air 
are  active  ;  it  is  very  slow  combustion,  and  although  heat 
is  produced  it  is  too  small  in  amount  to  alter  the  temperature 
of  the  structure  or  to  be  detected  by  a  thermometer.  It  is 
said  that  in  heaps  of  very  thin  scrap-iron  the  heat  due  to 
rusting  of  the  iron  accumulates  so  rapidly  that  the  tempera- 
ture produced  has  been  sufficient  to  set  them  on  fire.  This 
way  of  taking  fire  is  an  example  of  spontaneous  combustion  ; 
because  the  fire  starts  without  the  aid  of  any  outside 
lighting. 

Coal  is  often  stacked  in  heaps,  particularly  at  collieries 
and  stations,  in  the  open  air,  and  in  such  stacks  spontaneous 
combustion  has  been  known  to  occur.  It  has  often  been 
observed  that  these  stacks  will  blaze  up,  or  smoke,  at  several 
parts  after  a  shower  of  rain.  The  rain  is  the  cause  of  letting 
fresh  air  into  the  stack,  and  as  the  latter  passes  in  it  attacks 
the  coal  and  produces  sufficient  heat  to  start  a  blaze.  In 
summer  time  these  occurrences  are  fairly  frequent  owing  to 
the  warming  of  the  coal ;  stacks  are  often  whitewashed  in 
order  to  reflect  off  them  the  sun's  heat  and  so  remain  cool. 

Gob  fires  which  occur  in  pits  and  the  firing  of  hay- 
stacks afford  examples  of  spontaneous  combustion.  In  all 
these  cases  there  is  an  absorption  of  air  by  the  substance 
and  a  production  of  heat ;  when  the  heat  makes  the  substance 
hot  enough  it  bursts  into  flame. 

The  Transforming  Action  of  Heat, 

Watch  the  action  of  a  glowing  fire  on  a  piece  of  freshly 
thrown-on  coal  ;  if  the  coal  is  a  soft  variety  it  will  be  seen  to 
form  at  places  a  thick  tarry  liquid  and  gas  ;  the  latter  easily 
ignites  and  burns. 


4  An  Introduction  to  Mining  Science. 

Thus  heat  may  change  a  solid  into  liquid  and  gaseous 
substances.  It  is  important  to  notice  that  in  this  case  if 
the  liquid  and  gas  were  cooled  they  would  not  turn  back 
into  coal,  they  have  permanently  changed. 

Experience, 

The  water  as  it  boils  in  the  kettle  turns  into  steam,  which 
condenses  back  again  to  water  whenever  it  happens  to  cool,  as 
in  leaving  the  spout.  Water  will  in  frosty  weather  become  ice. 

This  experience  is  so  frequent  that  we  are  often  led  to 
neglect  its  full  teaching  and  meaning.  This  latter  one 
differs  from  the  previous  piece  of  experience ;  it  teaches  us 
that  the  substances,  steam  or  ice,  would  turn  back  into 
water  by  cooling  or  warming  respectively.  The  difference 
is  an  important  one  because,  although  produced  in  both 
cases  by  altering  the  temperature,  the  change  in  the  coal  is 
not  capable  of  being  reversed  ;  whereas  the  change  of  water 
to  ice,  or  steam  to  water,  is  capable  of  being  reversed  and 
the  stuff  started  with  reformed. 

Experience. 

The  oil  of  a  burning  lamp,  or  the  fat  of  the  lighted  candle 
is  turned  into  vapour,  which  ascends  the  wick  and  burns  into 
gases.  These  gases  mix  with  the  air. 

It  might  be  noticed  that  the  candle  fat  must  pass  into  a 
liquid  before  it  passes  up  the  wick,  but  it  would  be  quite 
impossible  after  collecting  these  gases  to  turn  them  back 
into  oil  or  fat.  There  are  plenty  of  examples,  to  be  found 
by  observation,  of  changes  going  on  in  solid  substances — 
heat  turning  them  into  liquids  or  gases.  The  most  com- 
mon changes  are  those  where  action  has  taken  place  and 
which  cannot  be  undone,  so  as  to  re-form  the  original  sub- 
stance. Let  us  give  a  short  consideration  to  the  burning 
of  the  gas  of  an  ordinary  room  ;  the  loss  of  smell  undergone 
in  the  burning  denotes  a  change.  Whatever  is  formed 
when  gas  burns  is  an  invisible  substance  and  therefore  is  a 
gas ;  it  must  also  be  incombustible,  otherwise  burning  would 
go  on  around  the  flame.  Two  substances  are  formed,  as 


Combustible  and  Incombustible  Substances.          5 

a  matter  of  fact,  odourless,  invisible  and  incombustible. 
It  is  plain  where  the  original  substance  cannot  be  re- 
formed that  the  character  has  been  completely  changed  and 
substances  differing  from  it  have  been  made.  Such  changes 
are  very  common,  and  we  might  speak  of  them  as  changes 
in  the  composition  of  a  substance ;  they  are  technically  called 
chemical  changes.  A  chemical  change  means  an  alteration 
in  composition. 


Experience, 

When  a  new  mantle  has  been  placed  in  position  on  an  in- 
candescent burner  it  is  set  fire  to  by  a  match  ;  there  is  vigorous 
combustion  and  an  unconsumable  mantle  left. 

This  procedure  burns  off  the  cementing  stuff  that  stiffens  the 
mantle  for  transit  purposes.  This  cementing  material  is  very 
inflammable,  and  affords  an  example  of  fairly  rapid  com- 
bustion. 

This  common  piece  of  experience  therefore  affords  us  an 
excellent  lesson  on  combustible  and  non-combustible  sub- 
stances. The  non-combustible  mantle  becomes  incandes- 
cent, i.e.  white  hot,  by  the  heat  of  the  combustible  gas  and 
therefore  gives  out  light. 

There  is  left  behind  the  non-combustible  material  of  the 
mantle  which  in  nature  is  very  closely  akin  to  sand,  also 
non-combustible.  It  may  differ  in  colour  from  ordinary 
sand,  but  the  yellow  colour  of  sand  is  easily  removed  by 
acid.  In  appearance,  and  in  not  being  combustible,  the 
mantle  is  much  like  lime,  but  it  is  a  nearer  relative  of  the 
sand  family  of  substances  than  of  the  lime  family. 

The  gas,  like  the  collodion  which  is  the  cementing 
material,  is  changed  into  invisible  substances  by  the  action 
of  heat  and  air,  but  the  mantle  undergoes  no  change  except 
that  it  increases  in  brittleness  with  use. 

It  is  important  that  we  should  fully  understand  all  the 
actions  which  go  on  when  a  substance  is  heated  ;  we  are  apt 
to  regard  the  moment  it  takes  fire  as  the  beginning,  but  it  is 
essential  that  we  should  know  that  action  is  going  on  before 
flame  and  fire  show  themselves. 


6  An  Introduction  to  Mining  Science. 

Air  and  Heat, 

It  has  just  been  stated  that  heat  and  air  act  in  changing 
substances,  e.g.  gas  and  collodion.  It  must  be  clearly  recog- 
nized that  although  they  act  together  and  jointly  they  act 
in  entirely  different  ways,  heat  prepares  the  way  for  the  air's 
action. 

Air  does  not  act  upon  everything  at  the  ordinary  tempera- 
ture, e.g.  it  is  not  until  the  temperature  of  coal  is  3^  times  that 
of  boiling  water  that  the  air  begins  to  make  it  burn.  It 
would  be  unfortunate  if  air  did  attack  everything  at  its 
ordinary  daily  temperature,  otherwise  no  structure  would  be 
safe.  When  heat  is  applied  to  a  body  it  is  the  signal  for 
the  air  to  prepare  for  attacking  it  as  soon  as  the  body  gets 
hot  enough. 

Robert  Hooke,  an  Oxford  chemist,  who  lived  in  the 
seventeenth  century,  said  "  the  air  is  the  universal  dissolvent 
of  all  combustible  bodies  "  ;  by  a  universal  dissolvent  Hooke 
meant  that  combustible  bodies  turning  as  they  burn  into 
other  substances — gases — disappear  from  view  as  they  pass 
into  the  air. 

Robert  Boyle,  who  lived  in  the  same  century,  specially 
interested  himself  in  combustion,  and  he,  jointly  with  Hooke, 
discovered  that  candles  would  not  burn  in  vessels  from 
which  all  air  had  been  exhausted.  It  cannot  be  too  deeply 
learnt  that  when  a  thing  is  completely  burnt,  the  air  cannot 
attack  it  further,  and  if  a  thing  will  neither  burn  nor  rust, 
the  air  is  indifferent  towards  it. 

The  air's  action  consists  in  attacking  the  different  con- 
stituents of  a  substance  and  changing  them.  The  change 
varies  with  the  nature  of  the  constituent,  e.g.  one  constitu- 
ent of  coal  gas  is  called  hydrogen  gas,  and  every  double 
particle  of  the  latter  gas  is  attacked  by  a  single  particle 
of  the  active  constituent  of  the  air ;  they  all  become  fixed 
firmly  together  and  do  not  again  separate.  Another  con- 
stituent of  coal  gas,  called  marsh  gas,  behaves  differently  ; 
its  five-fold  particle  splits  up  during  burning,  dividing  itself 
into  three  parts,  each  one  of  which  takes  up  a  single  or  a 
double  particle  of  air.  The  original  particles  may  be  illus- 
trated by  diagrams,  which  are  correct  in  number  of  particles 
but  grossly  exaggerate  the  size  of  the  particles  : — 


Combustible  and  Incombustible  Substances.          J 


oo  ooo  oo 


Double  hydrogen  Five-fold  marsh  Double  oxygen 

particle.  gas  particle.  particle  (the  air's  active 

constituent). 

When  the  attack  of  the  air  upon  the  particles  of  any  sub- 
stance commences  heat  is  produced  ;  the  active  constituent 
of  the  air  showers  its  particles  violently  and  at  a  great  speed 
upon  the  substance  making  it  hot.  The  action  is  very 
similar  to  the  blacksmith's  hammer  raining  its  blows  on  the 
anvil ;  both  anvil  and  hammer  become  hot,  but  there  is  this 
difference  that  when  a  particle  from  the  air  strikes  a  particle 
of  any  substance  and  produces  heat  these  two  particles 
become  at  once  firmly  adherent. 

That  heat  is  continually  produced  when  coal  gas  is  burning 
requires  but  little  effort  on  our  part  to  recognize.  Heat  is 
continually  produced  as  the  active  particles  attack  the  gas 
particles  and  this  turns  the  issuing  stream  of  gas  into  flame 
at  the  gas  jet. 

Experience, 

To  start  the  burning  of  gas  a  lighted  match  is  applied.  This 
starts  the  burning  and  then  any  more  gas  streaming  out  is 
ignited  by  the  burning  portion  ;  it  takes  the  place  of  the 
lighted  match. 

The  flame  is  handed  on  to  the  stream  of  particles  coming 
along  the  gas  pipe  as  they  appear  at  the  gas  burner,  they  get 
heated  by  the  gas  just  burnt,  and  at  once  start  burning. 

Compare  the  action  with  the  idea  expressed  in  Henry 
Newbolt's  lines  on  the  words  "Play  up  "  : — 

Bear  through  life  like  a  torch  in  flame, 
And  falling,  fling  to  the  host  behind. 

It  is  necessary  to  carefully  distinguish  between  heat  and 
air;  the  latter  consists  of  particles  which  have  weight,  and  in 
the  burning  of  gas  its  weight  is  increased  by  the  gas  particles 
taking  up  air  particles. 

Heat  is  not  a  substance  ;  it  is  a  rapid  trembling  of  the  par- 


8  An  Introduction  to  Mining  Science. 

tides  of  a  body,  and  when  the  body  is  cool  the  particles  have 
returned  to  a  fairly  quiet  and  placid  condition.  If  they 
became  quite  motionless,  entirely  at  rest,  the  body  would 
have  no  heat  in  it  and  therefore  no  temperature.  This 
latter  state  has  never  been  completely  reached  in  any  sub- 
stance. 

There  is  no  difference  in  weight  between  a  body  hot 
and  the  same  body  cold,  unless  in  the  heating  the  air 
has  attacked  it. 

It  is  often  said  that  "heat  can  be  seen  rising,"  as  in  the 
waviness  that  can  be  seen  over  a  lighted  gas  or  a  heated 
metal  surface,  e.g.  railway  lines.  As  the  air  comes  into  con- 
tact with  hot  gas  or  rail  it  gets  heated  and  rises ;  it  is  the 
heated  air  which  can  be  seen. 

Experiments  on  Combustible  and  Incombustible  Sub- 
stances, 

I.  Heat  in  the  Bunsen  flame  (Fig.  i)  a  length  of  the  following 
wires:  platinum,  iron,  and  copper. 
See  if  the  glow  of  the  wire  varies 
at  different  parts  of  the  flame. 


A  Try  and  estimate  the  tempera- 

ture of  the  glowing  wire  by 
its  colour,  using  the  following 
table  :— 

Rough  Estimation  of  Tem- 
perature by  Colour. 
Glow  just  visible,   520°   C.  ; 
dark  red,  700°  C.  ;  cherry  red, 

FlG    x  900°  C.  ;  bright  cherry  red,  1000° 

C.  ;    orange,    1 1 50°   C.  ;    white, 

1300°  C.  ;  dazzling  bluish  white,  1500°  C.  ;  electric  arc,  3500°  C. 
2.   Ignite  a  2-inch  length  of  magnesium  wire  holding  it  in  the 
flame  by  crucible  tongs,  and  compare  the  result  with  those  ob- 
tained in  the  previous  experiment. 

There  is  neither  gain  nor  loss  of  material  in  the  case  of 
the  platinum  wire,  as  could  be  shown  by  weighing  before  and 
after  the  experiment,  and  there  is  no  colouring  of  the  flame. 
The  platinum  wire  undergoes  but  one  change,  and  that  a 
temporary  one ;  it  glows  or  becomes  incandescent. 


Combustible  and  Incombustible  Substances.          9 

The  copper  and  iron  wires  will  undergo  further  changes 
than  that  of  glowing,  e.g.  the  copper  will  blacken.  These 
changes  will  be  permanent,  and  more  easily  seen  by  com- 
paring pieces  of  heated  and  unheated  wires.  If  a  vapour 
comes  from  the  wire  it  may,  or  may  not,  influence  the 
colour  of  the  Bunsen  flame.  Copper  vapour  gives  a  distinct 
green  colour  to  the  flame. 

The  Burning  of  Magnesium  Wire, 

This  metal  when  heated  in  air  burns  with  a  dazzling 
white  light,  largely  used  in  taking  flash-light  photographs. 
It  should  be  noticed  that  the  burning  of  the  metal  continues 
after  its  withdrawal  from  the  flame.  The  Bunsen  supplies 
the  heat  required  to  start  the  action,  but  that  required  to 
continue  the  burning  is  supplied  by  the  violent  action  going 
on  between  the  metal  and  the  air. 

When  the  light  of  the  burning  magnesium  has  died  away, 
there  remains  a  white  substance  having  the  original  shape 
of  the  metal.  Compare  its  properties  with  that  of  the 
original  metal ;  it  is  a  white  substance  instead  of  a  lustrous 
metal ;  a  fragile  body  instead  of  a  tough  one.  A  piece  of 
this  white  substance  held  in  the  Bunsen  flame  may  be  seen 
to  glow  in  the  dark,  but  it  does  not  give  out  a  dazzling  light 
nor  undergo  combustion. 

The  differences  in  the  action  of  heat  upon  platinum, 
copper,  magnesium,  and  iron  compels  us  to  arrange  all 
changes  into  two  classes  :  temporary  changes  and  permanent 
changes.  In  a  permanent  change  the  substance  changes 
its  composition ;  either  something  is  removed  or  added,  it 
is  plain  that  weighing  the  substance  before  and  after  the 
experiment  will  tell  us  which  has  happened.  Iron,  copper, 
and  magnesium  permanently  change  by  heating,  but  plati- 
num remains  unaltered  after  withdrawal  from  the  flame. 

Experiments  on  Solid  Substances, 

Heat  a  piece  of  the  following  substances,  holding  them  by  the 
crucible  tongs,  in  the  hottest  part  of  the  flame  (Fig.  i)  ;  notice 
any  effects  :  lime,  asbestos,  coal,  coke. 


lo  An  Introduction  to  Mining  Science. 

Asbestos  and  lime  will  glow  to  a  moderate  extent  in  the 
Bunsen  flame,  the  asbestos  may  even  show  signs  of  fusing, 
but  in  neither  case  will  a  vapour  be  given  off.  They  are 
examples  of  incombustible  substances  which  may  be  raised 
to  incandescence  by  heat.  Gas  fires  which  have  the  gas 
flame  playing  on  pieces  of  asbestos  leave  them  unburnt. 
The  lime  cylinder  on  which  the  hot  flame  plays  in  the 
oxy-hydrogen  flame  of  the  optical  lantern  is  unburnt,  it 
shows  the  incombustibility  of  lime.  The  oxy-hydrogen 
flame  has  a  temperature  of  2800°  C.,  it  raises  the  lime  to  a 
white-hot  incandescent  state  but  does  not  burn  it.  A  bril- 
liant white  heat  can  even  be  produced  at  1500°  C.,  or  about 
half  that  of  the  lime  cylinder  in  the  oxy-hydrogen  flame. 

Asbestos  contains,  as  constituents,  lime  and  also  the 
white  substance  formed  when  magnesium  burns.  The  two 
foregoing  substances  along  with  sand,  which  is  an  infusible 
substance,  are  the  three  constituents  which  have  been 
worked  up  by  nature  into  the  material  called  asbestos. 

The  action  of  heat  on  coal  and  coke  is  different  from  the 
foregoing ;  the  general  experience,  of  the  student  should  be 
utilized  in  interpreting  the  action.  Coal  will  give  off  gas 
and  smoke  as  it  does  on  the  fire,  the  former  being  very  easily 
ignited.  Coke  being  coal  from  which  all  fumes,  gas,  and 
smoke  have  been  driven  off  will  only  glow.  If  the  coke  is 
made  red  hot  then  it  may  burn  and  give  off  flame,  but  the 
flame  will  be  distinctly  different  in  appearance  from  the 
flame  of  coal. 

Experiments  on  Substances, 

Warm  separately  and  gently  a  small  quantity  of  each  of  the 
following  substances  in  a  porcelain  dish  resting  it  on  a  tripod  or  as 
shown  in  Fig.  2  :  petrol,  benzine,  petroleum,  vaseline,  paraffin 
wax.  Try  and  ignite  their  vapours.  Hold  a  glass  rod  in  the 
burning  vapour  and  note  any  result. 

The  five  foregoing  substances  are  chosen  because  they 
belong  to  the  same  family  of  compounds  as  marsh  gas,  this 
being  the  dangerous  constituent  of  fire  damp.  By  a  family 
of  compounds  is  meant  a  number  of  individual  substances 
which  behave  similarly  in  their  ways  and  made  up  of  the 
same  constituents.  This  paraffin  family,  of  which  there  are 


Combustible  and  Incombustible  Substances.        1 1 


many  members,  resemble  one  another  in  inflammability  or 
combustibility. 

Marsh  gas  is  a  gas,  as  its  name  implies,  and  if  mixed  with 
air  possesses  combusti- 
bility and  explosive 
power.  One-third  of 
coal  gas  consists  of 
marsh  gas,  and  as  a  com- 
bustible and  explosive 
substance,  when  mixed 
with  air,  coal  gas  is  well 
known. 

Petrol,  benzine  or 
benzoline,  and  petrol- 
eum are  liquids,  and 
therefore  heavier,  bulk 
for  bulk,  than  marsh 
gas.  Petrol  and  ben- 
zine are  more  dangerous 
than  petroleum,  because 
they  easily  pass  into  va- 
pour which  by  mixing 
with  air  becomes  in- 
flammable, and  would 
in  a  confined  space 
have  explosive  power. 


FIG.  2. — Apparatus  for  warming  small 
quantities  of  an  inflammable  liquid. 


If  air  at  the  ordinary  temperature  is  passed  over  petrol  the 
latter  evaporates,  and  a  mixture  of  air  and  petrol  vapour  is 
obtained ;  this  is  explosive.  This  mixture  is  applied  and 
used  in  petrol  engines  where  the  explosion,  i.e.  the  firing  of 
the  charge  of  vapour  and  air,  is  started  by  an  electric  spark. 

The  proportion  of  petrol  to  air  in  the  mixture  is  about 
nine  of  air  to  one  of  petrol. 

Petroleum  does  not  give  off  a  vapour  as  easily  as  petrol,  but 
its  explosive  power  is  often  exemplified  by  lamp  explosions 
in  houses.  This  is  on  account  of  its  vapour  mixing  with  air 
in  the  reservoir  of  the  lamp,  and  getting  over-heated  in  some 
way,  it  fires  and  shatters  the  lamp.  Suppose  a  wick  is  loose 
in  its  lamp  fitting  or  metal  chamber  and  by  reason  of  its 
shortness  it  is  not  dipping  into  the  oil.  The  wick,  unless 


12  An  Introduction  to  Mining 

thoroughly  extinguished,  may  burn  down  in  its  fitting  and 
so  fire  the  mixture  of  air  and  vapour  in  the  reservoir,  the 
air  having  found  its  way  into  the  reservoir  by  the  bad  fitting 
of  the  wick  in  its  metal  chamber. 

Vaseline  and  paraffin  wax  are  substances  still  less  liable 
when  heated  to  give  off  inflammable  vapour  than  petroleum  ; 
in  fact  it  would  be  more  accurate  to  say  they  give  off  a 
combustible  vapour  than  an  inflammable  one.  Vaseline  is 
a  good  example  of  a  semi-solid  substance. 

It  is  necessary  to  remember  that  explosions  cannot  occur 
unless  the  vapour  is  mixed  with  air,  and  they  are  not  likely 
to  be  damaging  ones  unless  the  firing  takes  place  in  a  closed, 
or  partly  closed,  space,  e.g.  a  room  or  a  mine.  Then  they 
can  only  occur  at  a  certain  temperature. 

In  our  experiments  on  inflammable  bodies  there  is  no 
danger  to  ba  feared  from  explosions  because  the  vapour  is 
ignited  in  an  open  space. 

Practical  Application  to  Mining, 

Combustion  in  its  various  forms  is  continually  taking  place 
in  the  mine.  It  may  occur  by  accident  or  design,  or  it  may 
be  the  result  of  one  of  those  processes  of  change  which  are 
constantly  taking  place  in  nature's  laboratory.  Let  us  con- 
sider these  causes  separately. 

The  accidental  burning  of  inflammable  material,  such  as 
candles  or  waste,  or  the  production  of  a  spark,  due  to  a 
defect  in  some  of  the  electrical  arrangements  of  the  mine, 
may  cause  the  timber  supporting  the  roof  to  take  fire  and 
possibly  the  coal  itself,  with  disastrous  results.  Fires  in 
mines  may  have  very  serious  consequences ;  they  are  very 
much  dreaded  by  those  who  take  part  in  the  management 
of  collieries.  In  addition  to  the  danger  from  the  fire  itself, 
there  is  danger  of  suffocation  by  smoke,  of  being  poisoned 
by  inhaling  the  gases  given  off  from  the  fire,  and  lastly,  the 
danger  from  falls  of  roof  caused  by  the  burning  of  the  timber 
supports. 

A  few  examples  of  serious  underground  fires  caused 
by  accident  may  be  given.  In  1908  a  fire  occurred  at 
Hamstead  Colliery,  near  Birmingham,  and  twenty-five  lives 


Combustible  and  Incombustible  Substances.        13 

were  lost.  The  miners  at  this  colliery  worked  by  the  light 
of  candles,  and  the  fire  was  caused  by  the  carelessness  of  a 
miner  who  on  taking  his  supply  of  candles  from  the  candle 
box  at  the  pit  bottom,  burned  off  his  bundle  instead  of 
cutting  it,  placed  the  smouldering  wick  back  into  the  box 
and  set  on  fire  the  whole  of  the  candles  in  the  box. 

In  1909  accidentally  setting  fire  to  a  load  of  hay  was  the 
cause  of  a  great  disaster  at  the  Cherry  Mine,  Illinois,  250 
lives  being  lost. 

In  1911  a  fire  occurred  at  Pinxton  Colliery,  Derbyshire, 
which  was  caused  by  the  fusing  of  an  electric  cable  in  a 
pump-room  in  the  side  of  the  shaft,  setting  fire  to  timber 
and  coal.  The  smoke  from  the  fire  was  very  pungent. 
The  fire  was  fought  by  men  wearing  rescue  apparatus  and 
eventually  got  under  control,  the  411  men  underground 
being  got  out  safely. 

Regulations  under  the  Coal  Mines  Act,  1911,  require  : 
"  That  no  person  shall  allow  any  burning  wick  or  part  of  a 
wick  or  other  burning  material  to  lie  about  in  the  mine, 
and  every  workman  on  leaving  his  working  place  shall  take 
his  light  or  lights  with  him  ". 

Where  candles  are  used  they  must  not  be  stored  in  the 
mine.  "All  candles  used  in  the  mine  shall  be  placed  in 
a  metal  holder  which  shall  be  of  such  a  design  that  when 
fixed  to  a  prop  the  flame  of  the  candle  cannot  set  fire  to 
the  work."  "Candles  looped  or  strung  together  shall  in  no 
circumstances  be  burned  off  below  ground." 

"  In  any  mine  or  part  of  a  mine  in  which  safety  lamps 
are  required  by  this  Act  or  the  regulations  of  the  mine  to  be 
used,  no  person  shall  have  in  his  possession  any  lucifer 
match  nor  any  apparatus  of  any  kind  for  producing  a  light 
or  spark  except  so  far  as  may  be  authorized  for  the  purpose 
of  shot-firing  or  re-lighting  lamps  as  authorized  by  an  order 
made  by  the  Secretary  of  State,  or  any  cigar,  cigarette,  pipe, 
or  contrivance  for  smoking." 

The  regulation  dealing  with  matches  and  smoking  con- 
trivances is  a  very  important  one.  A  large  number  of 
persons  are  prosecuted  every  year  for  breaches  of  this  regula- 
tion, and  a  number  of  accidents  have  been  due  to  this  cause. 
It  is  very  probable  that  the  majority  of  persons  who  offend 


14  An  Introduction  to  Mining  Science. 

in  this  way  are  quite  innocent  of  any  intention  to  do  so, 
but  this  fact  only  proves  the  need  for  the  greatest  vigilance 
on  the  part  of  the  management  of  the  colliery  and  by  the 
workmen  themselves. 

One  or  two  examples  from  reports  of  Inspectors  of  Mines 
showing  how  unconscious  breaches  of  the  regulations  might 
have  had  very  serious  results  will  be  both  interesting  and 
instructive. 

Some  miners  found  a  jacket  smouldering  as  it  hung  in  a 
gateroad.  The  fire  had  been  started  by  matches  which  had 
slipped  down  into  the  lining  of  the  coat. 

An  undermanager  on  going  into  a  slit  connecting  the 
intake  and  return  airways,  where  workmen  hung  their  clothing 
on  nails  driven  into  wood  battens  resting  on  brick  side  walls, 
discovered  the  remains  of  a  jacket  which  had  become 
ignited.  The  jacket  was  hanging  on  a  nail,  and  close  to  it, 
on  the  floor,  were  the  remains  of  another  jacket  in  a  red 
glow.  The  latter  had  evidently  been  the  first  to  take  fire 
and  had  set  fire  to  the  former  with  which  it  would  be  in 
contact  when  both  were  hanging  up.  The  battens  into 
which  the  nails  were  driven  had  taken  fire,  and  very  serious 
consequences  would  probably  have  resulted  if  the  fire  had 
not  been  discovered.  The  owner  of  one  of  the  jackets 
admitted  that  he  smoked  on  the  way  to  work  but  left  his 
pipe  at  the  surface  and  as  no  trace  of  a  pipe  was  found  in 
either  coat,  a  probable  explanation  of  the  occurrence  seems 
to  be  that  some  smouldering  ash  from  the  pipe  must  have 
remained  in  a  pocket  of  his  jacket. 

Combustion  is  necessary  and  desirable  for  giving  light  to 
the  miner,  but  the  use  of  candles  and  lamps  should  be  at- 
tended with  the  greatest  care  so  as  to  avoid  accident.  In 
shot-firing  we  have  another  example  of  necessary  combustion, 
and  in  this  case  also  careful  precautions  should  be  taken. 

A  very  important  class  of  mine  fires — those  due  to 
spontaneous  combustion — are  dealt  with  in  another  chapter. 

QUESTIONS. 

1.  Explain  why  the  incandescent  gas  mantle  and  the  carbon  fila- 
ment in  an  electric  lamp  do  not  burn  away  by.  using. 

2.  A  man  smokes  a  cigarette,  cigar,  or  pipe  by  drawing  air  through 


Combustible  and  Incombustible  Substances.        I  5 

it.     Will  there  be  any  differences  in  the  air's  composition  before  and 
after  the  drawing  through  ;  if  so,  what  are  they  ? 

3.  A  small  electric  fan  is  revolving  quickly,  and  it  is  found  that  as 
a  glowing  match-stick  is  brought  towards  it  the  colour  of  the  glow 
changes  from  red  to  yellow.     Explain  it. 

4.  Draw  up  a  list  of  substances  which  may  be  easily  ignited,  and 
another  list  of  things  which  cannot  be  ignited.     Then  draw  up  a  list 
of  things  which  are  between  these  two  extremes. 

5.  Which  of  the  following  phenomena  show  incandescence  without 
combustion  ? — 

Molten  iron  as  it  flows  out  of  the  furnace. 

A  red-hot  platinum  wire. 

A  red-hot  poker. 

An  asbestos  gas  stove  red  hot. 

A  coal  gas  flame. 

6.  In  South  Wales  some  people  mix  clay  or  lime  w'th  fine  or  small 
coal  making  a  ball  of  fuel.    What  part  of  the  ball  is  useless  as  fuel,  and 
why  ? 

7.  What  combustible  substances  are  taken  down  the  mine  every 
shift  by  the  miner  ?     Are  clothes  saturated  with  lamp  oil  likely  to  be 
dangerous  in  the  mine  ? 

8.  A  man  with  heavy  nails  in  his  boots  accidentally  kicks  a  stone  in 
the  mine  and  produces  a  shower  of  sparks.     How  do  you  account  for 
their  being  red  hot  ?     Is  such  an  action  dangerous  in  a  mine  ? 

9.  Which  would  be  the  best  wire  for  making  a  gas  mantle  identical 
in  shape  with  the  common  mantle  ? 

10.  Is  a  red-hot  fire  incandescent?     Does  it  differ  in  any  way  from 
a  red-hot  Welsbach  mantle  ? 

11.  Why  are  dishes  used  for  evaporating  liquids,  as  in  Fig.  2,  made 
of  porcelain  ?     Is  there  any  advantage  in  having  a  glaze  on  them  ? 


CHAPTER  II. 


THE  AIR:  ITS  CONSTITUENTS  AND  ITS  ACTIONS. 

IT  is  a  very  common  custom  to  blow  a  fire  if  it  shows  signs 
of  going  out,  the  blowing  being  done  by  the  bellows  or  by 
the  mouth.  This  helps  the  fire  to  burn  more  vigorously,  but 
at  times  it  has  to  be  blown  with  care.  If  there  is  but  little 
red-hot  coal  in  the  fire,  and  this  of  a  dull  red  colour,  then 
it  is  possible  that  strong  blowing  will  put  out  the  fire — the 
cold  current  of  air  takes  away  heat  and  so  the  red  glow  may 
disappear.  In  general  circumstances  if  we  start  blowing 
gently  the  glow  increases  and  passes  from  a  dull  to  a  bright 
red,  and  then  even  with  vigorous  blowing  the  coal  gets  well 
alight,  but  all  the  time  the  cold  air  has  been  robbing  the 
fire  of  heat.  The  pouring  of  a  stream  of  air  on  the  fire 
tells  us  that  the  air  is  in  some  way  helpful  to  combustion, 

for  the  fire  increases  in 
brightness  despite  the  cold 
air  taking  away  some  of  its 
heat. 

Experiment, 

Heat  a  bit  of  wood  char- 
coal in  a  porcelain  crucible 
supporting  it  on  a  tripod  by 
a  pipeclay  triangle  ;  have  no 
lid  on  the  crucible  and  ob- 
serve what  happens ;  take 
the  time  it  requires  to  burn 
away  completely.  It  will  be  completely  burnt  away  asi  soon  as 
the  black  colour  has  disappeared.  Heat  a  similar  amount  well 
covered  with  sand  the  same  length  of  time.  Remove  the  sand 
and  compare  the  result  with  the  previous  one. 

16 


FIG.  3. — Apparatus  for  showing  that 
exclusion  of  air  stops  combustion. 


The  Air :  its  Constituents  and  its  Actions.       ij 

Robert  Hooke,  the  Oxford  chemist,  performed  a  similar 
experiment  in  1665,  and  he  found  that  the  charcoal  re- 
mained  unconsumed  when  there  was  no  free  access  of  air, 
but,  as  Hooke  said,  "  when  it  comes  into  contact  with  free 
air  it  readily  burns  away  ". 

Underground  fires  when  removed  from  the  pit  in  tubs 
are  covered  by  a  layer  of  sand. 

Cutting  off  the  Air  Supply. 

In  schools  scholars  are  instructed  that  if  their  clothing 
should  catch  fire  the  best  thing  to  do  is  to  lie  on  the  floor 
and  roll  rapidly  over  and  over,  perform  what  a  child  calls 
tl  roly-poly  ". 

If  there  happens  to  be  any  good-sized  covering  at  hand, 
e.g.  a  rug,  carpet,  blanket,  or  coat,  then  it  should  be 
wrapped  round  the  burning  child  by  anyone  present,  then 
laying  the  child  on  the  floor  roll  it  over  and  over  gently. 

Now  it  is  plain  that  this  is  putting  a  visible  wrapper 
round  the  body  so  as  to  keep  the  air  from  the  burning 
clothes  and  so  smother  the  fire. 

Further  experiments  must  be  made  to  prove  that  the  air  is 
concerned  in  combustion. 

Experiment. 

Take  a  bottle  containing  phosphorus,  and  note  the  presence  r* 
of  water. 

The  best  method  for  obtaining  a  bit  of  phosphorus  from  the 
bottle  is  to  invert  it  on  the  hand  and  withdraw  a  piece,  which 
should  immediately  be  placed  in  water  in  using  a  porcelain  dish  ; 
also  fill  up  the  bottle  again  with  water.  Cut  with  a  knife 
the  piece  obtained,  keeping  it  under  water.  Having  obtained 
a  small  piece  of  the  substance  cut  it  in  two  parts.  All  cutting 
must  be  done  under  water. 

Dry  one  part  quickly  by  blotting  paper  and  place  it  in  a  dry 
vessel,  the  other  part  leave  in  the  vessel  containing  water. 
Notice  any  action  which  goes  on  in  the  vessel  where  the 
phosphorus  is  surrounded  by  air.  Write  down  any  inferences 
you  may  draw  from  the  experiment. 

The  experiment  teaches  us  that  white  fumes  come 
from  the  phosphorus  which  is  surrounded  by  air.  If  the 
experiment  is  allowed  to  continue  for  a  length  of  time  the 


1 8  An  Introduction  to  Mining  Science. 

vessel  would  fill  with  fumes.  The  air  is  attacking  the 
phosphorus  and  the  white  fumes  consist  of  a  new  substance 
made  from  the  air  and  the  phosphorus. 

The  water  in  the  second  vessel  cuts  off  air  from  the 
phosphorus  and  there  is  no  action. 

You  should  now  be  in  a  position  to  give  reasons  for  the 
method  adopted  in  cutting  and  storing  phosphorus. 

Lavoisier,  an  illustrious  French  chemist,  satisfied  himself 
by  experiment  in  1774  that  some  part  of  the  air  is  absorbed 
by  phosphorus  when  it  fumes  or  burns. 

Experiment, 

Collect  a  vessel  full  of  coal  gas,  by  holding  the  inverted  vessel 
over  an  unlit  gas  burner,  then  quickly  introduce  a  lighted  taper. 
Notice  carefully  the  action  of  the  gas  on  the  lighted  taper. 

The  vessel  is  held  upside  down  on  account  of  the  gas 
being  lighter  than  air.  The  gas  burns  at  the  mouth  of  the 
vessel  where  there  is  air,  but  the  taper,  which  burns  in  air, 
is  extinguished  as  soon  as  it  is  thrust  into  the  coal  gas. 

The  experiment  therefore  in  a  three-fold  way  shows  that 
air  is  necessary  for  combustion. 

Experience. 

The  blacksmith  in  reviving  his  fire  blows  air  through  it. 
The  house  fire  has  its  ashes  poked  away  so  as  to  brighten  it  up 
by  letting  in  air.  The  gas  used  for  lighting  purposes  burns  only 
when  it  has  passed  the  gas  nipple  and  comes  into  contact  with 
air. 

Smothering  Flame  by  Excluding    Air. 

If  a  lighted  taper  or  match  is  introduced  into  a  vessel 
containing  a  jar  of  carbon  dioxide  gas  the  light  is  ex- 
tinguished or  smothered. 

If  a  lighted  match  or  taper  or  other  lighted  thing  could 
be  put  into  a  gasholder  there  would  be  no  explosion, 
the  light  would  go  out.  As  there  is  no  air  there  can 
neither  be  ignition  nor  combustion. 

Experiment. 

Place  a  piece  of  washing  soda  or  a  bit  of  limestone  in  a  gas 
jar,  then  add  some  dilute  acid.  Effervescence  at  once  begins, 


The  Air :  its  Constituents  and  its  Actions.       ig 

due  to  carbon  dioxide  gas  being  liberated  from  the  solid  put  in 
the  jar.  Keep  the  jar  covered  until  the  effervescence  stops, 
then  put  a  lighted  taper  into  the  jar  ;  the  light  is  extinguished. 

The  gas  surrounds  the  light  on  all  sides,  the  air  supply  is 
entirely  cut  off  and  therefore  combustion  stopped.  Compare 
this  with  the  similar  experiment  with  coal  gas  on  p.  18. 

Experience. 

It  has  fallen  to  the  lot  of  most  people  to  take  off  the  kettle 
lid  and  look  inside,  using  a  lighted  match  to  see  if  the  water  is 
boiling.  If  the  water  is  hot  the  space  above  it  is  filled  with 
water  vapour  and  the  light  is  immediately  extinguished. 

The  lighted  match  is  cut  off  from  the  air  supply  and  it 
cannot  therefore  continue  to  burn.  The  action  of  water 
vapour  or  carbon  dioxide  or  coal  gas  is  precisely  similar  to 
surrounding  a  burning  body  by  a  tight-fitting  covering ;  the 
air  is  kept  away  by  the  invisible  gas,  or  the  visible  covering 
and  the  combustion  is  stopped. 

Smothering  a  Fire  by  Water  Vapour, 

How  does  water  act  in  extinguishing  a  fire  ?  Does  its 
vapour  help  in  the  action  ?  Help  is  given  in  two  ways : 
the  heat  of  the  fire  converts  the  water  into  vapour  and  the 
burning  body  gets  surrounded  by  a  cloak  of  it.  In  this  way 
as  water  vapour  does  not  support  combustion  the  fire  is 
smothered,  i.e.  it  can  get  no  air.  The  space  around  the 
burning  body  is  crowded  with  particles  of  water  vapour  and 
there  is  no  room  left  for  air  particles,  so  burning  cannot 
continue. 

Apart  from  the  smothering  action  there  is  an  abstraction 
of  heat  from  the  thing  burning  as  soon  as  water  is  thrown 
on  it,  and  this  tends  to  stop  the  burning.  The  heat  ab- 
stracted is  partly  used  up  in  making  the  water  hotter,  and 
partly  in  turning  some  water  into  steam. 

Smothering  a  Lamp. 

If  a  miner  finds  himself  in  an  atmosphere  containing 
"gas"  and  it  begins  to  burn  in  his  lamp,  he  should  not 
attempt  to  blow  it  out  because  he  is  feeding  it  with  air. 


2O  An  Introduction  to  Mining  Science. 

The  lamp  should  be  smothered  by  covering  all  air  holes 
with  cap,  coat,  or  any  other  available  covering;  this  effectu- 
ally "  smothers  the  lamp  "  by  cutting  off  air  which  is  vital 
to  burning. 

Experiment. 

Take  a  lamp  glass  and  fit  half  way  into  the  lower  end  a 
cork  from  which  about  one-third  of  its  area  has  been  removed 
as  wedge-shaped  pieces  around  the  circumference.  Fix  a  short 
piece  of  candle  on  the  cork,  either  by  melting  the  wax  or  a  nail 
penetrating  the  cork  and  candle. 

Light  the  candle  and  note  any  tendency  to  smoke  or  any 
unsteadiness  of  the  flame.  Now  fit  the  lamp  glass  on  the  cork 
and  see  if  any  differences  show  themselves  in  the  flame. 

Cover  the  upper  end  of  the  lamp  glass  by  a  cork  or  other 
covering,  and  close  by  a  cloth  the  openings  in  lower  cork.  Notice 
that  the  flame  is  extinguished. 

The  effect  of  the  lamp  chimney  is  to  draw  a  current  of 
air  through  it.  This  produces  a  greater  brightness  of  the 
flame,  and  the  tendency  of  the  candle  to  smoke  disappears. 
The  air  is  drawn  around  the  flame  and  this  brings  about 
more  complete  and  intense  combustion  and  more  light. 
The  current  of  air  also  brings  about  the  complete  combus- 
tion of  the  smoke ;  it  may  be  too  strong,  i.e.  too  rapid,  and 
the  brightness  of  the  flame  is  therefore  lessened,  the  yellow 
area  being  decreased. 

Experiment. 

Take  an  oil  lamp  and  light  it.  Partly  close  the  chimney  top 
by  moving  a  piece  of  cardboard  above  and  across  it ;  see  if  a 
position  can  be  obtained  where  the  flame  emits  more  light.  If 
there  be  such  a  place  the  chimney  normally  causes  too  much 
draught. 

The  stoppage  of  the  air  supply  by  placing  the  cardboard 
on  the  top  of  the  lamp  glass  would  cause  the  extinction  of 
the  flame. 

Experience. 

In  the  lighting  of  an  oil  lamp  the  increased  brightness  of  the 
flame  may  be  seen  immediately  the  chimney  glass  is  placed  on 


The  Air:  its  Constituents  and  its  Actions.      21 


the  lamp.     The  blocking  up  of  the  air  holes  by  dust,  dirt,  and 
oil  is  known  to  affect  the  light-giving  power  of  the  lamp. 

Boyle  and  Hooke's  experiment,  that  candles  would  not 
burn  in  vessels  from  which  all  the  air  had  been  extracted,  is 
not  an  easy  matter  to  repeat,  but  a  modification  of  it  may 
easily  be  performed. 

Experiment, 

Take  a  glass  vessel  called  a  bell  jar,  and  stand  it  on  the  bottom 
of  a  vessel,  which  should  be  large  enough 
in  diameter  to  allow  the  bell  jar  to  stand 
in  it ;  fix  in  a  3 -inch  piece  of  candle  as 
shown  in  Fig.  4.  Place  a  layer  of  water 
about  2  inches  deep  in  the  vessel,  light 
the  candle,  and  put  over  it  the  open  bell 
jar,  and  then  tightly  fix  in  the  stopper. 
Notice  any  effects  on  the  light  of  the 
candle,  repeat  the  experiment  to  see 
if  these  effects  again  happen. 

It  is  necessary  to  notice  that  in  the 
bell  jar  a  small  portion  of  air  has 
been  cut  off  from  the  atmosphere, 
and  although  the  candle  starts  well 
lighted  it  is  soon  extinguished. 

If  we  removed  the  stopper  of  the 


FIG.  4. — -Experiment  to 
show  that  air  is  neces- 
sary for  combustion. 


bell  jar  and  passed  a  tube  from  the  outside  air  through  the 
water  and  under  the  jar  into  the  space  where  the  candle  is, 
and  lighted  the  candle  again,  it  would  not  go  out.  It  would 
have  been  given  a  continuous  supply  of  air  and  therefore 
continue  to  burn.  We  understand  now  why  a  miner's  lamp 
is  always  provided  with  openings ;  it  is  to  allow  a  stream  of 
air  to  pass  through  and  so  keep  the  oil  burning. 

It  is  necessary  to  consider  further  this  stoppage  of  the 
burning  of  a  body  when  shut  up  in  a  small  quantity  of  air. 
The  same  result  will  happen  to  other  bodies.  Some  explana- 
tion Of  the  result  must  be  found. 

Experiment, 

Use  the  apparatus  as  shown  in  Fig.  5.  Cut  under  water 
a  small  piece  of  phosphorus,  about  the  size  of  a  pea,  an4  then 


22 


An  Introduction  to  Mining  Science. 


dry  it  quickly  between  blotting-paper.  Place  it  in  a  small 
porcelain  crucible  which  will  float  on 
the  water  in  the  bottom  vessel.  Over 
this  floating  crucible  containing  the 
phosphorus  place  the  open  bell  jar  and 
then  replace  the  stopper.  Notice  that 
the  water  inside  and  outside  the  bell  jar 
is  at  the  same  level.  Mark  this  level 
outside  by  a  strip  of  gummed  paper. 
Heat  a  long  piece  of  glass  tube,  or 
wire,  and  removing  the  stopper  touch 
the  phosphorus  with  the  heated  end. 
At  once  withdraw  the  tube  or  wire,  and 
replace  the  stopper.  Notice  all  that 
occurs. 


FIG.  5.— Apparatus  for 
finding  the  amounts 
of  oxygen  and  nitro- 
gen in  air. 


The  phosphorus  burns  fiercely,  but 
finally  goes  out,  and  the  jar  is  filled 
with  white  fumes.  Leave  the  jar  to 
cool,  notice  as  it  does  so  the  fumes  disappear  and  the 
water  rises  to  a  higher  level  inside  the  jar. 

The  action  has  apparently  resulted  in  a  loss  of  air  to  the 
bell  jar,  inasmuch  as  the  water  stands  at  a  higher  level ;  there 
is  now  less  space  occupied  by  the  air  in  the  jar. 

In  a  particular  experiment  it  was  found  that  the  jar  to 
start  with  had  140  cubic  inches  of  air  in  it :  after  the  action 
was  over  and  the  jar  again  quite  cold  the  gas  left  in  was 
only  112  cubic  inches,  so  obviously  28  cubic  inches  had 
disappeared. 


Continuation  of  the  Experiment, 

When  the  vessel  is  cold  and  the  fumes  have  dissolved  in  the 
water  notice  that  the  water  has  risen  inside  one-fifth  of  the 
height  of  the  jar.  Now  bring  the  outer  level  of  the  water  up  to 
the  inner  level  by  adding  water.  Introduce,  after  removing 
the  stopper,  a  lighted  taper  into  the  bell  jar  and  notice  it  is 
quickly  extinguished,  or  try  and  re-ignite  the  phosphorus  in 
the  crucible  ;  it  will  be  found  to  be  impossible.  Replace  the 
stopper  again. 

The  bell  jar  now  contains  an  invisible  gas  which  will  not 
allow  a  taper,  nor  the  phosphorus,  to  burn  in  it.  Although 


The  Air :  its  Constituents  and  its  Actions.      23 

like  air  in  being  invisible,  it  is  unlike  it  in  not  allowing 
bodies  to  burn.  This  invisible  gas  is  a  constituent  of  the 
air  and  amounts  to  four-fifths  of  the  whole.  Air,  there- 
fore, consists  of  two  parts  of  which  only  one  supports 
burning. 

It  appears,  then,  that  air  is  made  up  of  two  gases,  one 
supports  the  burning  of  the  phosphorus,  but  is  used  during  the 
burning  and  then  the  burning  stops  The  second,  which  is 
plainly  the  larger  part  of  the  air,  will  not  allow  the  taper  nor 
phosphorus  to  burn  in  it,  and  so  is  left  untouched. 

The  figures  given  on  the  preceding  page  will  help  us  to 
find  the  relation  between  the  amounts  of  the  two  different 
gases  which  make  up  air ;  they  show  that  one-fifth  of  the 
air  disappears  and  four-fifths  are  left  untouched.  This  we 
should  find  to  be  approximately  the  case  in  the  experiment 
performed.  Lavoisier  called  this  gas,  which  takes  part  in 
the  burning  of  substances,  oxygen ;  the  name  means  acid 
producer  because  many  substances  burning  in  air  take 
up  oxygen  and  produce  acids.  The  inactive  gas  which  is 
left  behind  is  called  nitrogen,  a  word  that  means  nitre  pro- 
ducer. Nitre  is  very  largely  used  in  explosives. 

The  experiment  detailed  above  will  give  fairly  accurately 
the  relation  between  the  volumes  of  oxygen  and  nitrogen, 
it  ignores  small  amounts  of  argon,  carbon  dioxide,  and 
moisture.  See  p.  37  for  further  details  of  substances  in 
air. 


Further  Knowledge  of  Oxygen, 

Joseph  Priestley,  a  native  of  Birstall,  Yorkshire,  discovered 
oxygen  in  1 7  74  in  the  substance  called  red  precipitate ;  he 
called  it  fire-air. 

By  using  a  powerful  "  burning  glass  "  he  found  that  when 
the  solid  substance  called  red  precipitate  was  strongly  heated  a 
gas  came  off.  In  this  gas  a  candle  burned  brilliantly,  and 
some  mice  put  in  it  became  very  active  in  their  movements. 
In  the  same  year  Scheele,  a  Swedish  chemist,  independently 
discovered  oxygen  by  heating  nitre,  he  may  have  preceded 
Priestley  in  the  discovery  of  it. 


24  An  Introduction  to  Mining  Science. 

Experiment, 

Take  a  hard  glass  tube,  place  in  it  a  small  quantity  of  the 
substance  called  red  precipitate,  now  called  oxide  of  mercury, 
and  then  strongly  heat  it  ;  hold  at  the  same  time  in  the  upper 
part  of  the  tube  a  glowing  splint  of  wood,  and  notice  that  the 
glow  will  burst  into  flame  as  the  oxygen,  after  splitting  away  from 
the  mercury,  passes  up  the  tube  (see  Fig.  6). 


FIG.  6. — Breaking  up  "red  precipitate"  by  heat;  notice  the  mercury 
collecting  on  the  tube. 

Free  and  Bound  Oxygen, 

The  oxygen  in  the  air  is  mixed  with  nitrogen,  the  particles 
have  a  free  and  independent  existence.  The  oxygen  in  the 
red  precipitate  is  united  to  mercury ;  both  mercury  and 
oxygen  are  in  bondage  to  each  other,  and  great  heat  is 
required  to  break  up  this  bondage.  This  bondage  is 
technically  called  chemical  union. 

In  rusting  and  burning  we  have  free  oxygen  attacking  a 
substance  with  the  result  that  this  free  oxygen  enters  into 
bondage  with  the  rusting  or  burning  substance  ;  in  this  state 
of  bondage  oxygen  is  not  capable  of  helping  either  rusting 


The  Air :  its  Constituents  and  its  Actions.       25 

or  burning.  Only  when  it  is  free  from  bondage  can  it  take 
part  in  attacking  a  combustible  substance. 

Bondage  or  chemical  union,  therefore,  brings  about  a 
change  in  the  actions  of  a  substance  ;  it  considerably  restricts 
its  activity. 

These  ideas  of  free  and  bound  oxygen  are  of  great  im- 
portance. Bound  oxygen  cannot  support  combustion,  it 
must  be  liberated  first. 

Lavoisier  puts  Together  the  Facts, 

Lavoisier  was  shown  the  results  of  Priestley's  experiments. 
He  had  himself  found  that  red  precipitate  was  formed  when 
quicksilver  (mercury)  was  gently  heated  in  air,  and  the 
weight  of  red  precipitate  obtained  was  greater  than  that  of 
the  quicksilver  taken.  Lavoisier  argued  that  the  gain  had 
been  brought  about  by  some  air  having  been  absorbed  by 
the  quicksilver.  The  quicksilver  had  been  rusted  by  its 
heating  in  the  air. 

Lavoisier  was  the  first  man  who  gave  a  true  explanation  of 
rusting  and  burning ;  in  each  case  the  oxygen  of  the  air  is 
attacking  the  body  and  changing  it.  In  rusting  there  is 
generally  no  flame  produced  but  there  is  heat ;  as  rusting  goes 
on  little  by  little  so  the  heat  is  produced  little  by  little.  In 
rusting  the  body  changes  its  appearance  but  remains  a  visible 
thing.  In  burning  there  is  a  fierce  attack  between  the  oxygen 
and  the  burning  body ;  heat  is  liberated  in  big  quantities, 
flame  is  produced  and  the  body  disappears  as  gases  into  the 
atmosphere.  The  conclusion  has  been  reached  that  oxygen 
is  the  great  supporter  of  combustion. 

Lavoisier  also  proved  that  during  burning  the  body  is  not 
destroyed,  but  only  altered  in  nature.  Soot,  smoke,  and 
ash  are  a  few  visible  evidences  of  the  alteration ;  the  great 
portion  of  the  body  goes  into  the  air  and  becomes  invisible 
gases. 

As  oxygen  is  necessary  for  the  combustion  of  bodies  it 
is  interesting  to  know  the  amounts  of  oxygen  which  there 
must  be  in  air  for  combustion  to  continue.  The  following 
figures  show  the  amounts  of  oxygen  left  in  air  when  the 
bodies  named  will  no  longer  burn  ;-— 


26  An  Introduction  to  Mining  Science. 

Candle  goes  out  when  oxygen  is  reduced  to  1 7  per  cent. 
Petroleum  „  „  ,,  „          17 

Marsh  gas  „  „  „  „ 

Coal  gas  „  „  „  „ 

Phosphorus         „  „  „  „ 


Oxygen  is  vital  to  life  just  as  it  is  to  burning ;  there  can 
be  no  life  without  free  oxygen ;  it  gets  into  the  lungs  by  our 
breathing  air,  from  the  lungs  it  finds  its  way  into  the  blood 
and  so  goes  wherever  a  blood  vessel  is  carrying  blood.  In 
the  case  of  breathing  it  is  found  that  the  oxygen  may  be 
decreased  in  the  air  breathed  to  14  per  cent,  and  yet  it  is 
just  as  good  as  ordinary  air  which  contains  21  per  cent. 

It  is  plain  then  that  when  the  candle  or  light  goes  out  in 
the  mine  for  want  of  oxygen  the  air  is  still  fit  for  a  man  to 
breathe  without  danger.  Miners  who  therefore  think  they 
have  had  a  narrow  escape  after  passing  along  a  road  which 
extinguishes  their  light  may  thus  be  deceived,  but  such  an 
atmosphere  should  be  considered  dangerous. 

Substances  Formed  by  the  Oxygen's  Attack, 

As  there  are  many  common  combustible  substances,  e.g. 
coal  gas,  candles,  oil,  and  coal  which  disappear  during  their 
combustion,  it  is  necessary  to  find  what  substances  are 
produced  in  these  changes  and  their  influence  on  the  purity 
of  the  air.  Further,  are  there  any  substances  which  might 
be  regarded  as  pre-eminently  combustible  substances;  in 
short,  what  is  it  the  oxygen  attacks  with  so  much  fierceness 
when  heat  and  flame  are  produced  ? 

When  a  body  burns  it  usually  completely  disappears. 
We  shall  therefore  have  to  deal  with  invisible  things,  and 
some  means  must  be  devised  to  render  them  visible  so  as  to 
prove  their  existence. 

Experience, 

It  is  not  difficult  to  notice  that  when  certain  substances  burn 
moisture  or  water  is  formed.  A  kettle  of  cold  water  or  a  flat  iron 
placed  on  the  gas  stove  soon  has  its  under  surface  covered  with 
moisture.  The  chimney  glass  just  after  being  placed  on  the  lamp 
or  gas  burner  shows  a  mist  qn  its  inner  surface.  In  shop  windpws 


The  Air :  its  Constituents  and  its  Actions.      27 


the  glass  often  shows  moisture  inside  when  the  gas  is  lighted, 
and  the  temperature  of  the  outside  air  is  low. 

The  explanation  of  the  foregoing  experience  is  that  water 
vapour  is  formed  when  gas  or  oil  burns  and  condenses  on  a 
cold  object.  As  the  burning  goes  on  it  heats  the  body  so 
much  that  no  moisture  can  stay  on  it,  and  it  therefore 
becomes  dry ;  moisture  is  still  being  formed  but  the  body 
has  got  too  hot  for  it  to  condense  to  water. 

Experiment, 

Turn  on  the  gas  and  unlighted  (see  Fig.  7)  show  that  no  mois- 
ture is  deposited  on  a  clean, 
dry  and  bright  glass  vessel 
held  over  it.  Light  the  gas 
and  hold  the  same  vessel 
high  above  a  small  flame  ; 
moisture  will  be  at  once  de- 
posited on  its  surface. 

Gas,  candles,  oil  lamps, 
fires  and  human  beings  give 
off  moisture  or  water  vapour. 
This  may  be  proved  by 
using  the  same  vessel  in  a 
clean,  dry  condition.  We 
should  expect  to  find,  with 
so  many  sources  making  it, 
water  vapour  as  a  constitu- 
ent of  the  air  apart  from  its 
origin  as  rain. 

In  all  these  combustible 
substances  there  is  a  con- 
stituent called  hydrogen. 
This  substance  is  attacked 


FIG.  7. — Experiment  with 
coal  gas. 


by  the  oxygen  and  both  get  bound  together.  Moisture  is 
made  by  the  binding  together  of  oxygen  and  hydrogen  par- 
ticles. Both  are  gases  when  free,  but  united  they  form  that 
very  common  substance  water. 

Water  vapour  in  the  atmosphere  is  largely  derived  from 
water  surfaces,  such  as  rivers,  seas,  etc. ;  the  amount  added 
by  combustion  and  breathing  of  human  beings  and  animals 
is  very  small  in  comparison,  On  the  other  hand,  in  closed 


28 


An  Introduction  to  Mining  Science. 


places,  such  as  mines,  rooms,  etc.,  the  amount  added  to 
the  air  by  combustion  and  breathing  is  of  the  greatest  im- 
portance. 

The  average  amount  of  water  vapour  in  the  air  is  i  '5  per 
cent,  i.e.  i-J-  cubic  feet  in  100  cubic  feet  of  air.  It  is  spread 
uniformly  throughout  the  air.  The  amount  of  water 
vapour  in  the  air  may  be  found  by  an  instrument  called  the 
wet  and  dry  bulb  thermometer — there  is  one  kept  at  every 
colliery,  so  make  yourself  familiar  with  it  if  possible. 

Fig.  8  shows  the  instrument ;  it  consists  of  two  thermo- 
meters, one  of  which — called  the  wet  bulb — has  its  bulb 
constantly  wet  by  drawing  up  water,  along  a 
wick,  from  a  small  bottle.  Notice  that  the 
reading  of  the  wet  bulb  is  lower  than  that  of 
the  dry  bulb,  52°  F.  and  60°  F.  respectively. 
This  means  that  the  temperature  of  the  air  is 
60°  F.,  and  that  the  lower  temperature,  52° 
F.,  of  the  wet  bulb  thermometer  is  caused  by 
water  evaporating  off  the  bulb  and  taking  away 
some  of  its  heat.  The  greater  the  evaporation 
the  drier  the  air  is,  and  the  lower  the  tempera- 
ture recorded  on  the  wet  bulb  thermometer. 
If  there  is  no  evaporation  then  the  air  is  filled 
with  moisture  and  the  wet  bulb  reads  the  same 
as  the  dry  bulb. 

The  following  hygrometer  readings  were  taken  on 
three  successive  days  in  the  Intake  and  Return  Air- 
ways of  a  Yorkshire  pit.  The  readings  of  the  Dry 
(D)  and  Wet  (W)  bulbs  are  in  Fahrenheit  degrees: — 

D.    W.  D.   W.  D.   W. 

Intake       .         51     47  58    53  54     49 

Return      .         73     68  75     73  73     68 


FIG.  8.  — 
Wet  and  dry 
bulb  ther- 
mometer, or 
hygrometer. 


Water  vapour  in  air  is  of  some  importance 
because  it  produces  a  feeling  of  discomfort 
and  stuffiness.  If  the  "  wet  bulb "  of  the 
hygrometer  in  a  pit  shows  a  temperature 
of  70°  F.  there  is  much  moisture  present,  and  the  mine, 
or  a  room,  will  be  uncomfortable  to  its  inhabitants,  but 
dry  moving  air  at  90°  F.  would  be  satisfactory  to  anyone 
working  therein. 

Watering  the  roadways  of  mines  increases  the  amount  of 


The  Air :  its  Constituents  and  its  Actions.      2  9 

water  vapour  in  the  air  and  this  decreases  a  man's  capacity 
for  work,  particularly  if  the  temperature  is  high. 

Moisture  is  a  waste  product  in  the  processes  known  as 
burning  and  living ;  it  is  not  the  only  one.  Another  substance 
is  an  invisible  gas  which  does  not  easily  turn  into  a  liquid 
as  water  vapour  does,  and  so  we  get  no  familiar  or  simple 
indications  of  its  presence  in  air. 

Experience. 

Many  substances  withdraw  moisture  from  the  air  and  so  in 
time  become  moist,  e.g.  impure  table  salt.  Other  substances, 
e.g.  lime  water,  withdraw  carbon  dioxide  from  the  air.  If  lime 
water  is  kept  in  an  unstoppered  bottle  or  an  open  vessel,  a  thin 
white  crust  forms  on  its  surface.  Also  lime  mixed  with  water,  as 
used  for  lime-washing,  will  after  standing  in  a  bucket  show  a 
white  skin  or  layer  on  the  water  surface. 

The  formation  of  this  thin  white  layer  is  due  to  lime 
withdrawing  carbon  dioxide  gas  from  the  air  ;  it  is  formed  in 
the  following  experiment. 

Experiment. 

Take  a  small  glass  vessel  and  pour  into  it  a  £  inch  layer  of 
clear  lime  water,  then  allow  it  to  stand  exposed  to  the  air  ;  a  thin 
whitish  layer  will  be  formed  on  its  surface. 

Lime  water  consists  of  lime  dissolved  in  water.  The 
lime  in  it  absorbs  from  the  air  the  gas  called  carbon  dioxide 
or  carbonic  acid,  and  from  the  two  substances  the  white 
layer,  called  lime  carbonate,  is  made.  The  name  is  intended 
to  denote  it  is  made  of  lime  and  carbon  dioxide. 

The  explanation  is  that  the  carbon  dioxide  particles  in  the 
air  are  caught  and  fixed  by  the  lime  particles  dissolved  in 
the  water,  and  the  two  form  on  the  surface  a  layer  of  white 
substance  called  carbonate  of  lime. 

The  layer  of  air  over  the  surface  of  the  lime  water  has 
carbon  dioxide  particles  in  it,  and  as  they  are  taken  out  by 
the  lime  particles  fresh  ones  come  from  the  upper  layers  of 
air  to  take  their  places,  and  these  in  their  turn  are  seized  by 
lime  particles.  One  particle  of  lime  can  only  seize  one 
particle  of  carbon  dioxide. 

This  explanation  should  help  to  show  us  that  the  particles 


3O  An  Introduction  to  Mining  Science. 

of  carbon  dioxide  are  not  at  rest ;  there  is  movement  until 
they  get  seized  by  the  lime  particles,  then  as  they  form  part 
of  a  solid  film  they  lose  their  power  of  wandering. 

If  lime  water  be  kept  in  a  well-stoppered  bottle  no  film  is 
formed.  There  will  be  a  few  carbon  dioxide  particles  in  the 
air  above  the  liquid,  but  their  number  is  so  few  that  they 
are  insufficient  to  form  a  film. 

A  Test, 

When  it  has  been  found  that  an  action  accomplished  by 
one  substance  is  not  done  by  any  other  substance,  then  when- 
ever this  action  occurs  we  may  be  quite  certain  that  this  one 
substance  is  doing  it.  Carbonic  acid  is  the  only  thing  that 
will  form  this  white  layer  with  lime  water,  and  therefore  we 
speak  of  lime  water  as  a  test  for  carbonic  acid  because  it 
affords  a  means  of  detecting  the  latter. 

If  we  were  to  breathe  upon  some  clear  lime  water  a  layer 
of  carbonate  of  lime  would  be  formed.  If  an  arrangement 
were  made  to  lead  the  air  coming  away  from  the  burning  of 
oil,  gas,  candles,  etc.,  into  contact  with  clear  lime  water,  the 
same  substance,  lime  carbonate,  would  be  formed.  There 
are  some  very  simple  ways  of  showing  that  combustion  and 
breathing  result  in  the  production  of  carbonic  acid. 

Experiments  on  the  Products  of  Breathing, 

1.  Breathe  on  a  cold  clean  glass  surface  ;  a  film  of  moisture 
will  be  distinctly  seen. 

2.  Fill  a  cylinder  with  water  and  invert  it  into  a  basin  of 
water  ;  now  take  a  piece  of  glass  tube,  place  one  end  under  the 
inverted  cylinder,  and  empty  the  lungs  by  blowing  through  it. 
See  Fig.  9. 

Add  a  small  amount  of  lime  water  to  the  expired  air  in  the 
cylinder  and  shake  gently  when  the  white  substance  will  be 
obtained. 

A  Simple  Way  of  Applying  the  Test, 

Take  a  length  of  glass  tubing,  say  6  inches,  and  place  one  end 
in  a  beaker  or  vessel  which  contains  a  layer  of  lime  water.  Blow 
through  the  lime  water  and  notice  it  becomes  white  owing  to  the 
carbonic  acid  in  the  breath  forming,  with  the  lime,  carbonate  of 
lime. 


The  Air:  its  Constituents  and  its  Actions.       31 


FIG.  g. — Collecting  a  cylinder  of  expired  air  by  displacing  water. 

The  Products  of  Combustion, 

Show  that  any  burning  body,  e.g.  gas,  candle,  oil,  taper,  match, 
gives  off  carbon  dioxide.     Hold  a  cylinder  over  the  flame,  but  not 


FIG.  10. — Showing  the  method  for  collecting  the  carbon  dioxide  formed 
during  combustion. 


An  Introduction  to  Mining  Science. 


in  contact  with  it,  to  catch  the  products  of  combustion,  then  add 
lime  water  and  shake.  If  convenient  the  burning  body  may  be 
put  in  the  cylinder. 

If  the  cylinder  is  dry  it  will  become  visibly  misty  as  soon 
as  it  is  held  over  the  burning  body ;  this  shows  that  moisture, 
or  water  vapour,  is  also  produced  during  combustion. 

Experiment, 

Establish  by  collecting  coal  gas  in  a  dry  cylinder,  holding  it 
as  in  Fig.  10,  the  absence  or  presence  of  carbonic  acid  in 
unburnt  gas  by  the  above  test. 

Coal  gas  contains  no  moisture,  but  it  may  contain  some 
carbon  dioxide. 

The  foregoing  experiments  have  dealt  with  carbon  dioxide 
mixed  with  air,  but  the  quantities  of  the  former  are  not 
very  large  ;  there  is  only  5  per  cent  of  carbon  dioxide  in 
expired  air.  Now  if  we  want  to  find  exactly  what  carbonic 
acid  can  do,  it  is  plain  that  the  gas  must  be  obtained  by 

itself,  i.e.  free  from  all  other 
gases,  even  air.  Limestone 
or  marble  contains  44  per  cent 
of  its  weight  of  carbon  dioxide 
in  the  bound  condition,  and 
an  acid,  e.g.  nitric  or  hydro- 
chloric, will  liberate  the  gas 
from  the  limestone. 

Liberation    of   Carbon    Di- 
oxide from  Limestone. 

Take  a  flask  (see  Fig.  1 1 )  or  a 
wide-mouthed-bottle,  and  fit  it 
with  a  cork  through  which  a 
thistle-head  tube  and  a  bent  tube 
pass.  Place  gently  some  limestone 
into  the  flask  and  then  fit  in  the 
cork.  Pour  some  dilute  hydro- 
chloric acid  down  the  thistle-head 
with  a  • 

d     H  r          tube  ;  as  soon  as  it  comes  into 

teads  theVgas    contact  witn  tne  limestone  carbon 
into  the  cylinder.  dioxide  is  liberated  and  passes  out 

of  the  bent  tube  into  the  collecting 
vessel.     It  is  now  possible  to  find  what  carbon  dioxide  can  do. 


The  Air :  its  Constituents  and  its  Actions.       33 
Actions  of  Carbon  Dioxide  of  Importance  in  Mining. 

i.  Collect  ajar  of  carbon  dioxide  by  letting  the  gas  flow  into 
it,  prove  its  presence  by  a  lighted  taper.  A  lighted  taper 
held  in  the  mouth  of  the  jar  will  go  out  when  the  jar  is  full. 
Pour  this  jar  full  into  another  jar  and  prove  the  transference 
by  a  light  (see  Fig.  12). 


FIG.  12. — Pouring  carbon  dioxide  into  a  jar  full  of  air ;  the  air  is 
expelled. 

2.  Fill  a  jar  to  the  brim  with  carbon  dioxide ;  prove  it  is  full. 
Insert  a  pipette,  or  tube,  into  the  jar  so  as  to  reach  the  bottom 
and  fill  it  by  sucking  up  some  gas.  Find  by  a  lighted  taper  if 
there  is  air  at  the  top  of  the  jar,  and  carbon  dioxide  at  the 
bottom. 

Some  carbon  dioxide  will  have  been  removed  in  the 
pipette  and  air  will  go  into  the  jar  as  the  carbon  dioxide 
surface  sinks.  Imagine  the  action  and  the  result  from  your 

3 


34  An  Introduction  to  Mining  Science. 

knowledge  of  what  you  would  see  going  on  in  the  jar  if 
filled  with  water ;  it  is  precisely  the  same  action. 

3.  To  show  that  carbon  dioxide  is  heavier  than  air  counter- 
balance a  dry  beaker  on  one  pan  of  a  balance,  then  disturb  it 


FIG.  13. — Pouring  a  jar  of  carbon  dioxide  into  a  beaker  full  of  air ;  the 
air  is  displaced  by  the  heavier  carbon  dioxide. 

by  allowing  carbon  dioxide  to  flow  in  to  the  beaker  to  displace 
the  air,  as  shown  in  Fig.  13. 

These  experiments  show  that  carbon  dioxide  is  heavier 
than  air ;  it  is  about  i-j-  times  heavier,  and  by  reason  of  its 
heaviness  it  falls  to  the  bottom,  or  floor,  of  vessel,  or  room. 
Do  not  think  that  after  falling  it  will  remain  there ;  as  it 
falls  some  particles  are  lost,  but  all  will  in  time  disperse, 
each  individual  particle  moving  away  on  its  own  account. 
If  a  pond  were  being  stocked  with  fish  a  crowd  of  a  few 
hundred  might  be  thrown  in  all  at  once,  but  each  fish  would 
soon  begin  to  move  about,  and  finally  they  would  spread 
all  over  the  pond.  This  is  what  the  carbon  dioxide  particles 
do ;  the  action  is  called  diffusion. 

Gas  particles,  of  whatever  nature  or  kind  they  are,  move 
about,  and  so  it  is  impossible  to  keep  gas  particles  in  one 
place  unless  it  be  perfectly  closed,  i.e.  "air  or  gas  tight". 
This  expression  tells  us  that  in  ordinary  life  it  is  recognized 
that  gas  particles  will  escape,  but  it  is  not  so  widely  recog- 


The  Air :  its  Constituents  and  its  Actions.       35 

nized  that  if  some  escape  others  like  them  or  of  a  different 
nature  go  in  to  take  their  places. 

Experience, 

"  Keep  the  bottle  tightly  corked  "  is  an  instruction  often  given 
with  reference  to  a  liquid  in  a  bottle. 

The  liquid  easily  gives  off  its  particles  as  vapour,  and 
they  are  usually  the  essence  of  the  liquid.  If  the  bottle  is 
kept  corked  they  cannot  get  away  and  so  the  liquid  keeps 
its  strength.  If  the  bottle  is  left  uncorked  then  in  time  all 
the  liquid  passes  off  as  vapour,  made  up  of  particles  of 
the  substance  dissolved  in  the  liquid  and  particles  of  the 
liquid  itself,  and  air  takes  their  place  in  the  bottle. 

The  Diffusion  of  Carbon  Dioxide, 

Fill  a  cylinder  with  water  and  then  fill  one-tenth  of  it  with 
carbon  dioxide,  then  let  in  air.  This  may  be  done  by  bringing 
the  cylinder  in  an  inclined  position  to  the  surface  of  the  water 
and  then  letting  the  air  flow  in  at  a  part  of  the  cylinder's  mouth 
held  just  above  the  surface  of  the  water.  Take  a  sample  of  this 
gas  and  show,  by  lime  water,  it  contains  carbon  dioxide  mixed, 
diffused,  or  dispersed  throughout  the  cylinder. 

The  sample  may  be  taken  by  pouring  a  small  quantity  of  the 
gas  into  a  beaker  of  lime  water. 

This  experiment  shows  that  the  layer  of  carbon  dioxide 
does  not  remain  at  one  end  of  the  cylinder ;  the  particles 
disperse  or  diffuse  through  the  air  so  becoming  uniformly 
mixed  with  the  air.  Compare  it  with  the  illustration  of  fish 
in  a  pond. 

Extinction  of  Light  by  Carbon  Dioxide. 

Light  a  candle  and  pour  a  cylinder  full  of  carbon  dioxide  on 
to  it. 

Place  a  small  quantity  of  a  combustible  liquid  in  a  porcelain 
crucible  (see  Fig.  14),  ignite  the  liquid  and  pour  upon  it  ajar  of 
the  gas. 

A  light,  if  dependent  upon  anything  undergoing  combus- 
tion, cannot  continue  to  burn  unless  it  is  supplied  with  air. 

Fire  Extinguishers. 

Carbon  dioxide,  by  its  heaviness,  its  incombustibility,  and 
its  power  of  stopping  combustion,  is  used  for  extinguishing 

3* 


36  An  Introduction  to  Mining  Science. 

fires.  It  could  be  used  for  smothering  a  lamp  in  the  mine  if 
a  store  of  the  gas  were  kept  so  as  to  be  poured  on  to  a  lamp 
at  any  moment.  Probably  you  have  heard  of  a  miner's  lamp 
being  extinguished  by  "  black-damp  "  in  a  mine  ;  this  damp 
contains  much  carbon  dioxide. 

There  are  several  methods  of  storing  the  gas  for  fire 
extinction ;  one  is  to  force  the  gas  into  steel  cylinders,  and 
by  use  of  a  nozzle  and  tap  a  stream  of  the  gas  may  be 
played  on  to  a  burning  body.  The  gas  will  become  a  cloak 


FIG.  14. — Extinguishing  a  burning  liquid  by  using  a  vessel  full  of 
carbon  dioxide. 

to  the  fire  and  so  shut  off  the  air  from  the  flames,  so  the 
fire  is  bound  to  be  extinguished. 

It  is  useful  in  small  fires,  particularly  such  as  occur  in 
many  households,  it  is  most  effective  if  they  are  on  the  floor, 
for  the  gas  is  likely  to  fall  by  its  heaviness. 

If  the  fire  were  a  burning  piece  of  celluloid  or  any 
article  made  of  celluloid,  of  which  there  are  many,  even 
cinematograph  films,  carbon  dioxide  would  be  quite  useless 
for  its  extinction.  We  shall  find  why  later  on  in  the  book  ; 
water  would  be  the  only  extinguishing  agent. 

A  Few  General  Matters, 

There  are  different  amounts  of  carbon  dioxide  in  town 
and  country  air;  in  town  air  it  may  be  as  much  as  6  cubic 


The  Air :  its  Constituents  and  its  Actions.      37 

feet  of  carbon  dioxide  in  10,000  cubic  feet  of  air,  but  in 
country  air  there  is  only  half  this  quantity  in  10,000  cubic 
feet  of  air.  These  figures  stated  as  percentages  will  give  : — 

Town  air,  '06  per  cent  of  carbon  dioxide. 
Country  air,  -03       „  „ 

Town  and  country  air  are  always  trying  to  become  equal  in 
their  amounts  of  carbon  dioxide,  but  cannot  do  so  owing  to 
the  large  quantities  of  the  latter  gas  produced  in  towns. 

Expired  air,  just  as  it  comes  from  the  lungs,  contains  5 
per  cent  of  carbon  dioxide,  but  the  carbon  dioxide  does  not 
remain  in  this  air  after  expiration,  it  immediately  diffuses 
into  the  air  around  the  human  being.  It  is  therefore 
plain  that  there  must  be  plenty  of  fresh  air  supplied  in  order 
that  this  5  per  cent  may  be  so  diluted  with  fresh  air  that  it 
becomes  practically  free  from  carbon  dioxide.  The  produc- 
tion of  carbon  dioxide  in  mines  by  men  and  animals,  also 
in  small  quantities  by  combustion,  and  sometimes  its  supply 
from  old  workings,  leads  to  the  necessity  for  a  constant 
stream  of  fresh  air  passing  through  the  mine  by  way  of  the 
downcast  shaft. 

The  following  table  shows  the  average  composition  of  the 
air  as  it  passes  into  the  downcast  shaft  of  the  mine  : — 

Oxygen      .         .         .20*65  per  cent. 
Nitrogen    .  .77-11        „ 

Argon  ...  -80  „ 
Carbon  dioxide  .  .  -03  „ 
Water  vapour  .  .  1-41  ,, 

The  air  as  it  leaves  the  upcast  shaft  will  not  have  the 
same  composition.  Beyond  the  carbon  dioxide  and  water 
vapour  produced  by  combustion  and  respiration  there  will 
be  gases  given  off  by  explosives,  by  underground  or  gob 
fires,  and  fire-damp  escaping  from  the  rocks  and  coal  face. 
All  these  gases  will  mix  with  the  ventilating  current  of  air 
as  it  passes  along  the  airways  and  so  find  their  way  to  the 
upcast  shaft  and  out  of  the  mine. 

It  is  plain  from  the  table  that  the  air  is  a  mixture  of  gases, 
and  in  the  mixture  nitrogen  predominates.  Many  of  the 
gases  known  as  fire  damp,  black  damp,  etc.,  are  mixtures 


An  Introduction  to  Mining  Science. 


of  different  gases  with  one  predominating  constituent. 
These  gases  we  shall  have  to  study  ;  some  of  them  differ 
from  the  gases  of  the  atmosphere  in  being  combustible,  and 
therein  lies  their  great  danger. 

Practical  Application  to  Mining. 

The  benefit  of  the  improved  combustion  obtained  by 
placing  a  chimney  over  the  light  is  strikingly  shown  in  Hail- 
wood's  Combustion  Safety  Lamp  which  is  illustrated  below. 
The  addition  of  the  chimney  and  internal  glass  has  increased 


FIG.  15. — Hailwood's  com- 
bustion lamp. 


FIG.  16. — Photograph  showing  chim- 
ney, A,  and  internal  glass,  D. 


the  lighting  power  of  the  lamp  from  one-half  to  about  one  and 
a  half  candle  power.  This  is  a  very  important  improvement 
in  view  of  the  fact  that  miners'  nystagmus,  which  is  said  to 
arise  from  eye  strain  caused  by  insufficient  light,  is  rapidly 
on  the  increase. 

It  has  already  been  pointed  out  that  when  a  safety  lamp 
becomes  filled  with  burning  gas,  i.e.  when  gas  fires  in  the 


The  Air :  its  Constituents  and  its  Actions.      39 


lamp,  it  should  be  smothered  out  by  closing  up  all  the  air 
holes  by  means  of  which  air  enters  the  lamp.  It  is  not 
generally  known  among  young 
students  that  some  lamps  pos- 
sess two  air  inlets,  the  usual  one 
at  the  bottom  of  the  bonnet 
and  another  one  lower  down. 
A  sketch  of  such  a  lamp  is 
given  showing  the  air  inlets  and 
the  direction  of  the  air  currents. 
When  smothering  out  such  a 
lamp  care  should  be  taken  to 
cover  up  both  the  inlets. 

Reference  has  been  made  to 
the  hygrometer,  and  the  accom- 
panying illustration  (Fig.  18) 
shows  a  portable  instrument  for 
use  in  mines. 

With  the  ordinary  type  of 
hygrometer,  or  wet  and  dry 
bulb  thermometer,  the  bulbs 
must  be  placed  some  distance 
apart  causing  the  instrument  to 
be  rather  bulky.  A  new  form  of 
hygrometer  designed  for  mining 
work  is  the  psychrometer  (Fig.  19)  in  which  the  thermometers 
are  placed  close  together.  By  means  of  a  handle  fitted 
to  a  spindle  attached  to  the  framework  the  instrument  may 
be  rotated,  bringing  the  thermometers  into  better  contact 
with  the  air  and  giving  a  quicker  reading. 

Respiration   and  the  Portable  Breathing  or  Rescue 
Apparatus, 

In  exploring  a  mine  after  an  explosion  or  in  fighting  a 
mine  fire  the  advantage  of  an  apparatus  which  enables  the 
wearer  to  breathe  fresh  air  and  to  be  independent  of  the 
mine  atmosphere  will  be  readily  seen. 

The  types  of  breathing  apparatus  in  use  may  be  divided 
into  three  classes  : — 

i.  The  air  from  the  lungs  passes  into  a  receptacle  con- 


FIG.  17. — Sketch  of  lamp  with 
two  air  inlets. 


4O  An  Introduction  to  Mining  Science. 

taining  certain  substances  which  are  attacked  by  the  expired 
air  causing  oxygen  to  be  liberated.  This  oxygen  is  breathed 
by  the  wearer  of  the  apparatus. 

2.  Liquid  air  is  placed  in  a  box  or  pack  carried  on  the 


FIG.  18.— Photograph  of  pit  hygro-      FIG.  19. — Photograph  of  psychro- 
nieter.  meter. 

back  of  the  wearer  of  the  apparatus.  The  heat  of  the  body 
causes  the  liquid  air  to  evaporate  and  it  is  then  breathed  in 
the  ordinary  way.  A  sufficient  supply  to  last  for  two  or 
three  hours  may  easily  be  carried. 


The  Air :  its  Constituents  and  its  Actions,      41 

3.  The  carbon-dioxide  expired  from  the  lungs  is  ab- 
sorbed by  caustic  soda  or  caustic  potash  carried  in  a  suit- 
able case  or  box.  The  air,  which  is  now  pure  but  lacking 
in  oxygen,  passes  on  to  be  breathed  again,  but  before  reach- 
ing the  mouth  of  the  wearer  of  the  apparatus,  oxygen  from 


FIG.  20. — Diagram  of  portable  breathing  or  rescue  appara- 
tus :  compressed  oxygen  type. 

A,    Oxygen   cylinder;    B,   Caustic  soda  chamber;   C,  Indicator;   D, 

Oxygen    regulating    tap;    E,    Breathing    bag;    F,     Headpiece     or 

helmet. 

a  cylinder  carried  on  the  back  is  added,  making  the  air 
quite  fit  and  safe  to  breathe. 

In  all  types  of  breathing  apparatus  it  is  necessary  to  have 
(i)  Some  means  of  covering  the  nose  and  mouth  so  that 
the  outside  atmosphere  may  not  be  breathed.  (2)  A 


42  An  Introduction  to  Mining  Science. 

breathing  bag  to  enable  the  wearer  to  inspire  or  expire 
a  full  breath  and  to  properly  empty  or  fill  his  lungs. 

This  bag  is  usually  divided  into  two  parts. 

It  is  also  desirable  that  an  indicator  should  be  provided 
by  means  of  which  the  wearer  of  the  apparatus  is  able  to 
measure  his  supply  of  oxygen  from  time  to  time. 

Up  to  the  present  the  use  of  the  breathing  apparatus  has 
been  chiefly  confined  to  exploration  work  after  explosions 
and  to  extinguishing  fires  in  mines.  The  apparatus  is  too 
heavy  for  spare  sets  to  be  carried  in  for  the  purpose  of 
bringing  out  persons  who  might  be  alive  and  uninjured  in 
the  working  of  the  mine  not  traversed  by  the  explosion. 

Attention  is  now  being  given  to  the  perfecting  of  a 
lighter  type  of  apparatus  to  be  used  for  this  purpose.  It 
will  not  have  the  capacity  of  the  larger  type,  but  will  be 
sufficiently  large  to  enable  in  many  cases  a  man  to  walk 
from  the  workings  to  a  place  where  the  air  is  fit  to  breathe. 

The  Coal  Mines  Act  requires  that  rescue  stations  to 
serve  groups  of  collieries  shall  be  provided  where  men  from 
the  various  collieries  may  be  trained  in  the  use  of  the 
apparatus  and  in  other  matters  which  it  is  desirable  that  a 
member  of  a  rescue  brigade  should  know. 

QUESTIONS. 

1.  Describe  an  experiment  to  show  that  a  so-called  empty  vessel  is 
not  empty. 

2.  When  iron  is  rusting  in  air  state  what  is  happening  to  (i)  the 
air,  (2)  the  iron. 

3.  A  combustible  substance  was  placed  in  a  closed  vessel  contain- 
ing air  and  then  heated.      Will  there  be  any  change  in  the  weight  of 
(i)  the  air  in  the  vessel,  (2)  the  whole  apparatus  ? 

4.  How  could  you  prove  that  the  gas  liberated  by  heating  oxide 
of  mercury  is  identical  with  the  oxygen  of  the  air  ?     Does  the  oxygen 
of  the  air  require  liberating  from  any  substance  ? 

5.  Three  oxide   of  mercury  samples  made   in  different   countries 
were   found  to   contain  mercury  and   oxygen  in  the   proportions   by 
weight  of  100  to  8  respectively.      Do  you  think  there  is  anything  re- 
markable in  this  substance  always  having  its  constituents  in  the  same 
proportions  ?     Give  reasons  for  your  conclusions. 

6.  How  could  you  arrange  an  experiment  to  show  that  the  air  is 
concerned  in  burning  and  breathing? 

7.  Compare   the  properties    of   nitrogen   with    the   properties   of 
oxygen.     What  remarkable  properties  does  phosphorus  possess  ? 


The  Air :  its  Constituents  and  its  Actions.      43 

8.  Give   three   simple    and   successful  methods   of  smothering  a 
small  outbreak  of  fire. 

9.  Draw   up  a  list  of  metals  on  which  air  has  no  action  at  its 
ordinary    temperature.      Mention    two   substances   upon   which    air 
quickly  acts. 

10.  Give  a  short  account  of  the  scientific  work  of  Lavoisier. 

11.  A  human  being  gives  out  carbon  dioxide  gas.      Prove   this 
statement  by  experiment  and  say  what  is  its  origin  in  the  body. 

12.  A  saucer  of  water  is  placed  in  the  air  and  it  is  found  on  a 
particular  day  that  no  water  is  lost  by  evaporation.     Would  there  be 
any  difference  in  the  readings  of  the  wet  and  dry  bulb  thermometers 
on  this  day  ? 

13.  Consider  the  wet  and  dry  bulb  temperatures  given  on  p.  28, 
then  explain  why  the  readings  of  the  intake  and  return  airs  differ. 

14.  A   hygrometer   hangs  in  a  bathroom  which  is  full    of  water 
vapour.     Will  there  be  any  difference  in  the  readings  of  the  ther- 
mometers ? 


CHAPTER  III. 


AIR  CURRENTS  AND  HOW  THEY  ARE  CAUSED. 

IT  has  been  shown  that  the  air  of  a  room  or  a  mine  has 
moisture  and  carbonic  acid  added  to  it  by  the  presence  in 
it  of  human  beings,  animals,  and  burning  gas,  oil,  or  candle. 
For  the  purposes  of  health  these  added  substances  must  be 
cleared  out  of  mine  or  room.  To  bring  about  this  result  ad- 
vantage is  taken  of  air  movements,  as  free  as  possible  from 
objectionable  characters  such  as  a  too  high  speed  or  too  big 
a  rush,  so  as  not  to  produce  winds  and  draughts.  The  fire 
is  a  means  of  creating  air  movement  in  a  room. 

Experiment. 

Take  a  lighted  match,  or  a  candle,  and  move  it  up  from  the 
fire  to  the  top  of  the  fire  grate  ;  notice  the  great  pull  on  the  light 
as  the  highest  part  of  the  grate  opening  is  reached  ;  it  may  be 
sufficient  to  blow  out  the  light. 

Use  a  smouldering  piece  of  paper  which  is  giving  off  smoke, 
and  with  door  and  windows  closed  see  if  the  following  currents 
are  present  in  a  room. 

In  the  room  near  the  fire  (F)  find  the  current  of  air  which 
will  draw  the  smoke  of  the  paper  along  with  it. 


W 


FIG.  21. — Method  of  mapping  the  air  currents. 

At  the  windows  (W)  the  smoke  may  be  carried  away  from  them, 
and  also  on  the  floor  at  the  door  (D) ;  the  keyhole  of  the  door 
should  be  tried  for  a  current  passing  through  it. 

44 


Air  Currents  and  how  they  are  Caused.         45 

A  diagram  of  the  room  showing  the  position  of  doors 
and  windows  should  be  made,  and  the  arrows  put  in  the 
diagram  according  to  the  direction  of  the  currents.  It  is 
possible  that  the  direction  of  the  currents  may  differ  from 
those  given  in  the  diagram ;  in  any  case  the  results  of  an 
experiment  must  be  recorded  as  found. 

Experiment. 

Slightly  open  a  door  which  leads  from  a  room  into  a  passage. 
The  door  must  only  be  slightly  ajar.  Find  the  direction  of  the 
air  currents  at  the  top  and  bottom  of  the  doorway  by  using  a 
lighted  match  or  candle.  If  the  door  fits  badly  then  the  direc- 
tion of  the  currents  may  be  found  in  the  two  positions  with  it 
closed.  The  room  and  passage  will  no  doubt  vary  in  tempera- 
ture ;  their  temperatures  should  be  taken  so  as  to  make  the  experi- 
ment complete. 

In  a  particular  classroom  it  was  found  by  experiment  that 
the  bottom  of  the  doorway  was  an  inlet  for  cold  air  and  the 
top  an  outlet  for  the  air  of  the  room.  The  ceiling  of  this 
room  was  2  feet  higher  than  its  doorway ;  the  room  had  a 
temperature  of  65°  F.  and  the  passage  54°  F. 

The  explanation  of  these  currents  of  air  passing  through 
the  room  is  based  upon  the  fact  that  air  gets  lighter  as  it  is 
heated  and  is  then  pushed  along  by  the  heavier  air  behind 
it,  which  in  its  turn  gets  heated  and  so  is  pushed  forward. 
There  is  thus  a  continuous  flow  of  air,  i.e.  a  current  from 
the  outside,  where  the  air  is  fresh  or  pure,  to  the  inside 
where  it  gets  charged  with  more  or  less  moisture  and 
carbonic  acid. 

Heated  air  also  rises  by  the  same  cause,  and  consequently 
is  generally  found  towards  the  ceiling  of  the  room. 

Experiment, 

Take  a  sand  tray  and  place  some  sand  on  it ;  fix  it  on  a  tripod 
and  put  it  over  a  Bunsen  burner,  but  have  the  flame  turned  low 
so  that  it  is  entirely  under  the  tray.  When  the  tray  gets  hot  a 
quivering  of  the  air  can  be  seen  above  it ;  it  is  hot  air  rising. 
Smouldering  paper  giving  off  smoke  will  visibly  prove  the  rising 
of  the  air. 

If  a  thermometer  be  held  well  above  the  tray  it  will  show  a 
rise  of  temperature,  but  if  it  is  held  at  the  same  distance  to  the 
side  of  the  flame  there  will  be  little,  if  any,  rise  of  temperature. 


46  An  Introduction  to  Mining  Science. 

The  rising  of  air  on  heating  may  be  shown  by  experiment, 
for  this  the  temperatures  of  a  room  at  different  heights 
should  be  found. 

Experiment. 

Take  a  Fahrenheit  thermometer  and  fix  it  upright  on  the  floor 
of  the  room  away  from  any  source  of  heat.  Read  its  temperature. 

Repeat  the  experiment  with  the  thermometer  about  6  feet 
above  the  floor,  and  then  near  the  ceiling. 

The  room  is  supposed  to  be  lighted  by  gas  and  all  doors  and 
windows  closed. 

In  each  case  the  thermometer  must  be  given  two  or  three 
minutes  to  attain  the  temperature  around  the  position  stated  ; 
it  should  not  be  touched  on  the  bulb  by  the  hand  of  the  experi- 
menter. 

See  if  your  readings  warrant  you  in  saying  that  the  greater 
the  height  of  the  position  of  the  thermometer  the  higher 
the  temperature  of  the  air. 

The  explanation  of  the  results  again  depends  upon  the 
air  becoming  lighter  as  its  temperature  increases  ;  this  lighter 
and  hotter  air  is  pushed  up  to  the  ceiling  of  the  room.  This 
rising  is  not  due  to  the  tendency  of  heat  to  rise  but  to  the 
effect  of  heat  upon  air  ;  heat  increases  the  air's  volume  and 
it  therefore  decreases  the  weight  per  cubic  foot.  A  cubic 
foot  of  air  at  the  freezing-point  of  water  has  a  weight  of 
•08  Ib. ;  if  it  were  heated  to  2f  times  the  temperature  of 
boiling  water  it  would  become  2  cubic  feet,  and  therefore 
its  weight  per  cubic  foot  '04  Ib. 

In  gases  and  liquids  the  lighter  substance,  or  the  lighter 
part  of  the  substance,  will  always  be  on  the  top,  e.g.  oil  and 
water  ;  air  and  water ;  hot  water  and  cold  water  as  in  the 
hot-water  cylinder. 

A  Preliminary  Inquiry. 

Take  a  vessel  called  a  graduated  cylinder  ;  so  called  from  the 
graduations  or  divisions  on  the  vessel  (see  Fig.  22).  Compare 
it  with  a  cylinder  not  graduated,  and  note  its  advantages  for 
measuring  a  quantity  of  water  or  other  liquid.  If  the  graduated 
cylinder  is  numbered  like  the  one  in  Fig.  22,  then  it  is  called  a  100 


Air  Currents  and  how  they  are  Caused.         47 


C.C. 


--eo 


c.c.  cylinder  ;  the  symbols  c.c.  stand  for  cubic  centimetres.    The 
amount  of  water  lying  between  any  two 
neighbouring  graduations  is  i  c.c. 

If  the  100  c.c.  of  water  were  weighed 
it  would  be  found  to  weigh  loo  grams  ; 
therefore  I  c.c.  of  water  weighs  I  gram. 

The  simplicity  of  the  French  system 
of  weights  and  measures  is.  evident 
from  this  cylinder,  inasmuch  as  either 
a  weight  or  a  volume  of  any  liquid  may 
be  got  by  its  use  if  we  know  the  weight 
of  i  c.c.  of  the  liquid. 

Suppose  you  had  a  vessel  given  you 
exactly  the  size  of  Fig.  22,  then  it 
would  hold  up  to  the  top  graduation 
almost  4  c.c.  of  water.  This  gives  you 
an  idea  of  the  volume  represented  by 
the  statement  "4  c.c.". 

Air  and  its  Weight. 


A  previous  paragraph  has  spoken  of 
the  weight  of  the  air ;  it  is  important 
that  a  simple  experiment  for  obtaining  its  weight  at  the 
temperature  of  the  room  should  be  performed.  As  air  is 
not  very  heavy  it  will  be  an  advantage  to  state  the  weight 
in  grammes ;  i  grm.  is  the  unit  of  weight  in  the  French 
system.  The  volume  must  therefore  be  stated  in  cubic 
centimetres ;  i  c.c.  is  the  unit  of  volume.  As  air  expands 
on  being  heated  a  stated  volume  must  get  lighter  if  heated. 

One  thousand  c.c.  of  air  weigh  1*293  grm«  at  tne  freezing- 
point  of  water,  but  if  it  is  increased  to  a  volume  of  2000  c.c. 
then  1000  will  weigh  "6465  grm. ;  this  would  happen  if 
it  were  heated  to  2|  times  the  temperature  of  boiling  water. 
As  the  temperature  of  the  room  in  which  you  work  is  a  little 
higher  than  the  freezing-point  of  water,  the  weight  you  obtain 
should  not  differ  much  from  1*293  Srm-  Per  100°  c.c. 

To  Show  Air  has  Weight, 

Prepare  a  cylindrical  tin  vessel  (a  canister  will  be  found 
suitable),  4$  or  5  inches  long  by  3  inches  diameter,  by  boring  a 


FIG.  22. 


48  An  Introduction  to  Mining  Science. 

hole  in  the  lid  and  soldering  in  an  ordinary  bicycle  tyre  valve. 
Fit  the  lid  in  position,  carefully  solder  it  on,  and  see  that  the 
seams  of  the  canister  are  perfectly  airtight.  The  canister 
may  be  immersed  in  water,  after  pumping  in  air,  to  see  if  it  is 
airtight.  Slacken  off  the  valve,  to  ensure  that  there  is  no  excess  of 
air  in  the  canister,  and  carefully  balance  the  dry  apparatus  on  the 
pan  of  a  balance.  Remove  the  canister,  tighten  up  the  valve  and 
connect  an  ordinary  cycle  tyre  pump.  Give  eight  to  ten  (or 
more)  strokes  of  the  pump  and  replace  the  canister  on  the  scale 
pan.  It  will  no  longer  be  balanced  by  the  original  weights  but 
will  have  increased  in  weight  due  to  the  additional  air  ;  ascertain 
the  weight  of  the  air  pumped  into  the  canister. 

It  will  be  necessary  to  have  the  canister  dry  and  carefully 
weighed,  before  and  after  the  pumping  in  of  air,  if  we  are  to  find 
the  weight  of  a  volume  of  air. 

In  a  particular  experiment  with  a  tin  canister  fitted  up  as 
suggested,  the  following  weighings  in  grammes  were  ob- 
tained : — 

Weight  of  canister  after  pumping      87*33 
Weight  of  canister  before  pumping      87-05 

Weight  of  air  added          -28  grm. 


To  Find  the  Weight  of  1000  c,c.  of  Air, 

To  ascertain  the  volume  of  the  air  pumped  in  fill  a  trough  (or 
other  suitable  vessel)  with  water.  Fill  with  water,  and  invert  in 
the  trough  (as  for  gas  collecting)  a  glass  vessel  large  enough  to 
receive  the  volume  of  air  which  has  been  pumped  into  the 
canister.  Hold  the  valve  beneath  the  surface  of  the  water  under 
the  mouth  of  the  collecting  vessel,  slacken  off  slowly  so  as  to 
allow  all  the  added  air  to  be  collected.  Measure  the  volume,  and 
from  the  figures  calculate  the  weight  in  this  manner : — 

To  find  the  volume  of  the  -28  grm.  of  air  it  was  collected 
as  described  above  and  a  gum  label  placed  on  the  outside 
of  the  collecting  vessel  level  with  the  surface  of  contact  of 
water  and  air.  The  remaining  water  was  emptied  out  and 
then  water  poured  in  as  far  as  the  gum  label.  This  water 
was  then  measured  by  using  a  TOO  c.c.  cylinder. 


Air  Currents  and  how  they  are  Caused.         49 

The  following  result  was  obtained : — 

Cubic  centimetres  of  air,  218. 

The  weight  of  i  c.c.  will  be  — ^  and  this  multiplied  by 
1000  will  be  the  weight  of  1000  c.c. — 1*28  grm. 

Further  Study  of  Air  Currents. 

In  these  experiments  on  the  movement  of  air  by  its 
being  heated  some  difficulty  will  have  been  experienced  in 
following  the  movements  on  account  of  the  invisibility  of 
the  air ;  flame  and  smoke  have  been  used  to  detect  its 
movements.  One  experiment  given  on  p.  45  dispenses  with 
flame  and  smoke,  and  uses  the  fact  that  heated  air  flickers ; 
this  is  often  erroneously  stated  to  be  "  heat  rising  ".  This 
phenomenon  of  flickering  forms  in  one  way  or  another  very 
common  experience. 

Experience. 

In  a  large  hall,  church,  etc.,  get  a  position  with  the  light  from  a 
window  in  line  with  your  view  of  the  gas  fittings  ;  if  the  gas  is  lit 
for  warming,  currents  of  air  will  be  seen  rising  from  the  burners. 

On  a  hot  day  look  along  a  railroad  and  heated  air  will  be  seen 
rising  from  it. 

Notice  the  chimney  of  a  foundry  when  no  flame  is  seen,  hot  air 
along  with  other  gases  often  will  be  seen  rising  out  of  it. 

These  currents  conveying  heat  may  easily  be  seen  in  water 
or  other  liquids,  and  an  experiment  with  water  will  help  us 
to  realize  what  goes  on  in  a  gas  (see  p.  97). 

Experiment, 

Fix  a  U  tube  by  a  clamp  to  a  retort  stand.  Make  the  tube 
by  bending  a  piece  of  glass  tubing  (see  following  paragraph). 
When  cool  three-fourths  fill  it  with  water.  Warm  the  U  tube  at  the 
right-hand  bend,  but  do  not  let  the  flame  touch  the  glass.  The 
rising  of  a  heated  water  current  may  be  shown  by  dropping  into 
the  tube  a  crystal  of  permanganate  of  potash  just  after  warming 
the  bend. 

Cutting  and  Bending  a  Piece  of  Glass  Tubing. 

Glass  tube  may  be  cut  by  making  a  file  mark  on  it,  and 
then  breaking  it  back  at  the  mark  in  the  same  manner  as  a 
stick  or  pencil  could  be  broken  in  two  parts  at  a  mark. 

4 


50  An  Introduction  to  Mining  Science. 

Take  a  burner  of  the  type  shown  in  Fig.  23,  and  a  piece 


FIG.  23. 
of  glass  tubing   12  inches  long. 


FIG.  24. 
up  and  carries  the  heat  with  it. 


Place  the  tubing  about  5 
inches  from  one  end  in 
the  yellow  part  of  the 
flame ;  hold  it  as  shown 
in  Fig.  23  and  turn  it 
round  so  as  to  soften  the 
glass  equally.  When  the 
tubing  begins  to  soften 
control  its  bending  until 
it  has  bent  through  a 
right  angle  as  shown  in 
Fig.  24.  Now  repeat  the 
operation  at  5  inches  from 
the  other  end.  A  tube 
shaped  like  the  letter  U 
will  be  obtained ;  its  sharp 
edges  may  be  rounded  off 
by  heating  them  as  shown 
in  Fig.  24. 

We  have  found  that 
when  air  is  heated  it  rises 
Later  on  it  will  be  shown 


Air  Currents  and  how  they  are  Caused.         51 

by  experiment  that  this  heating  of  air  makes  it  expand  and 
become  lighter ;  the  rising  up  is  due  to  its  being  pushed  up 
by  the  heavier  and  less  heated  air.  It  should  be  noticed 
that  the  chimney  flue  of  an  ordinary  room  is  an  updraught 
shaft,  the  lighter  air  being  forced  up  by  the  flowing  in  of 
heavier  air  from  the  room  and  house. 

Mines  have  been  ventilated  by  having  a  furnace  at  the 
bottom  of  the  upcast  shaft  (see  Fig.  25).     The  fire  causes 


FIG.  25. — Illustrating  mine  ventilation  by  furnace :  A,    C,   are  the 
shafts  ;   B,  the  main  airway. 

the  air  in  the  shaft  C  to  become  lighter,  and  heavier  air 
falling  down  the  shaft  A  pushes  it  along  and  takes  its  place. 
The  air  passing  down  the  shaft  A  is  guided  into  various 
parts  of  the  mine  before  it  reaches  the  upcast  shaft. 

Furnaces  are  not  now  largely  used  for  ventilating  mines, 
but  the  dimensions  of  one  in  actual  use  should  be  interesting, 
it  is  situated  near  the  bottom  of  the  upcast  shaft.  These 
dimensions  are  :  length  of  furnace  60  feet,  breadth  1 1  feet. 

To  produce  an  updraught  and  downdraught  the  follow- 
ing experiment  should  be  made  : — 

Experiment, 

Take  a  large  flask  and  fill  with  smoke  by  charring  some  paper 
inside.  Cork  it  loosely  and  let  the  flask  cool ;  it  will  lose  no 
smoke,  then  after  removing  the  cork  and  fitting  a  piece  of  card- 
board into  the  mouth  of  the  flask,  as  a  partition,  place  under  it  a 

4* 


52  An  Introduction  to  Mining  Science. 

small  flame.     A  current  of  air  will  pass  into  the  flask  and  sweep 
out  the  smoke.    See  Fig.  26,  A,  B,  for  the  shape  of  the  partition. 

The  following  experiment  shows  another  way  of  producing 
draughts  : — 

Experiment, 

•  A  lamp  glass  is  fitted  with  a  piece  of  cardboard  A,  B,  cut  in 
the  shape  of  a  T.     The  base  of  the  lamp  glass  stands  on  a  piece 


FIG.  26. — Showing  an  arrangement  for  experimentally  producing  upcast 
and  downcast  currents. 

of  cardboard,  or  wood,  and  carries  a  short  piece  of  candle.  In 
finally  fixing  the  glass  over  the  lighted  candle  keep  it  slightly  to  one 
side  of  the  T  partition.  Show  by  using  a  lighted  match  or  taper 
(see  Fig.  26)  that  up  and  down  currents  are  produced. 

Look  around  the  classroom  and  see  if  there  is  a  long 
rectangular  box  on  the  wall,  called  Tobin's  tube,  see  Fig.  27. 
There  may  be  one  let  into  the  wall  with  an  iron  flap  which 
opens  into  the  room ;  if  there  is  perform  the  following  experi- 
ment : — 

Experiment. 

Hold  a  light  at  the  top  of  the  tube  and  notice  if  there  is  a 
current  of  air  deflecting  the  light— it  should  be  deflected  away  from 
the  wall  on  account  of  the  tube  being  an  upcast  shaft. 

Wherever  air  is  flowing,  no  matter  how  the  flow  is  pro- 
duced, it  is  moving  to  a  place  where  its  weight  per  cubic 


Air  Currents  and  how  they  are  Caused.         53 


foot  is  less.  As  soon  as  any  two  parts  of  the  atmosphere  have 
different  weights  per  cubic 
foot  a  draught  or  wind  is 
produced.  When  there  is  no 
draught  or  wind  the  weight 
per  cubic  foot  of  the  air  is 
the  same  everywhere.  Weight 
makes  a  substance,  exerts 
pressure,  therefore  read  the 
foregoing  sentences  through 
using  the  word  "  pressure " 
instead  of  the  phrase  "weight 
per  cubic  foot ".  It  is  easily 
concluded  that  the  heavier 
cubic  foot  of  air  must  exert 
the  greater  pressure  on  ac- 
count of  its  greater  weight. 

FIG.  27.— -Tobin's  tube. 

Experience, 

A  strong  wind  blowing  across  a  chimney-pot  improves  the 
draught  of  the  chimney,  see  Fig.  28.  This  is  due  to  the  aspirating 
force  of  the  wind  which  creates  Jess 

pressure  in  the.  flue  by  clearing  out  >  WIND 

some  air  and  so  more  air  rushes  up 
the  chimney. 

It  is  important  to  notice  that 
light  air  is  often  spoken  of  as  rare- 
fied air,  or  less  dense  air  ;  the  idea 
is  just  the  opposite  to  that  which 
is  meant  by  compressed  air  or 
more  dense  air.  The  method  of 
heating  air  so  as  to  make  it  lighter, 
so  starting  its  flow,  has  been  applied  to  mines,  but  is  now 
replaced  by  the  use  of  a  large  wheel  called  a  ventilating  fan. 
This  fan  is  situate  at,  or  near  to,  the  top  of  the  upcast  shaft ; 
it  acts  by  lightening  or  rarefying  the  air  of  the  upcast  shaft. 
The  action  of  the  fan  should  be  easily  understood,  because  we 
have  learnt  by  fanning  our  face  that  a  draught  can  be  pro- 
duced by  movement.  Every  boy  knows  that  if  he  wafts  a 
card  before  a  fire  he  will  draw  the  smoke  of  the  fire  towards 


FIG.  28. 


54  An  Introduction  to  Mining  Science. 

him;  the  action  starts  a  draught  in  opposition  to  theupdraught 
of  the  chimney  and  finally  overcomes  it.  A  space  containing 
rarefied  air  is  produced  as  the  card  moves  along ;  the  rarefied 
air  will  be  at  the  back  of  the  card,  i.e.  in  the  place  from 
which  the  card  moves,  and  into  this  space  the  heavier  air 
moves  along  with  its  smoke. 

Experiment, 

Take  a  glass  tube  about  i  foot  long  and  a  J"  diam.  and  place  it 
in  a  vessel  of  water  ;  then  blow  strongly  across  the  open  end  of  the 
tube  and  watch  for  any  variation  in  the  height  of  the  column  of 
water.  The  water  may  be  coloured  to  see  its  movements.  Fig. 
28  gives  the  corresponding  natural  action. 

The  explanation  is  based  on  the  sweeping  out  by  the 
current  of  some  air  in  the  tube  and  the  pressure  or  weight 
of  the  air  on  the  water  surface  in  the  tube  becoming  slightly 
less,  than  the  full  outside  air  pressure  drives  up,  slightly,  the 
water  column. 

Experiment  on  Disturbances  of  Air, 

Open  or  close  a  door  quickly,  leaving  plenty  of  time  between 
each  action,  and  find  the  direction  in  which  a  candle  flame  is 
moved  by  the  opening  and  closing. 

Rarefied  Spaces, 

If  we  consider  such  fast-moving  things  as  tram-cars,  motor- 
cars, or  trains,  we  may  recall  to  mind  that  when  moving  at 
a  great  speed  we  have  seen  paper  and  dust  lifted  up  and 
carried  along  for  a  distance.  This  is  due  to  a  disturbance 
of  the  air  ;  as  the  travelling  body  changes  its  position  quickly 
it  leaves  a  space  containing  rarefied  air,  and  into  this  the 
surrounding  heavier  air  rushes.  It  is  said  the  paper  is 
sucked  along  by  the  train  or  car,  whereas  really  it  is  swept 
forward  by  the  onrushing  heavier  air  finding  its  way  towards 
the  rarefied  air  space  and  filling  it  completely. 

Some  cyclists  maintain  that  it  is  easier  to  ride  when  behind 
a  motor-car  on  account  of  getting  into  the  "  suck  "  of  it, 
which  really  means  that  you  get  at  your  back  the  air  rushing 
in  to  fill  the  place  vacated  by  the  car,  and  so  you  are 
helped.  It  is  practically  a  wind  at  your  back.  It  is  im- 
portant, therefore,  to  remember  that  the  air  may  be  rarefied 


Air  Currents  and  how  they  are  Caused.         55 

not  only  by  heating  it  but  by  a  body  passing  through  it  at 
a  big  speed.  If  a  wheel  carrying  vanes  on  its  outer  rim 
could  be  kept  revolving  at  a  big  speed  it  would  throw  the 
air  away  from  it,  and  the  surrounding  air  by  its  greater  pres- 
sure would  flow  towards  the  wheel  again  in  its  turn  to  be 
hurled  away. 

Illustration, 

Imagine  a  big  crowd  of  people  standing  at  the  gates  of  a 
football  ground  and  then  the  gates  are  opened.  The  people 
scatter  in  all  directions  after  passing  in,  that  is,  the  crowd  be- 
comes rarefied,  their  places  are  taken  by  other  parts  of  the  crowd 
and  these  in  their  turn  spread  out.  The  pushing,  or  pressure,  of 
the  crowd  and  the  scattered  parts  are  totally  different  :  the  pres- 
sure at  the  gates  is  the  greatest  and  just  inside  it  is  the  least. 
In  this  way  the  crowd  by  its  pressure  moves  to  where  the  pres- 
sure is  less.  It  is  so  with  air  particles  filling  up  a  rarefied  space  : 
a  huge  crowd  by  their  pressure  rushes  the  few  in  the  rarefied 
space  away  and  then  occupy  it. 

Practical  Application  to  Mining, 

Ventilation  in  mines  is  necessary  to  renew  the  air  used 
up  in  the  process  of  breathing,  but  there  are  other  things, 
such  as  the  high  temperature  of  the  rock  in  deep  mines,  the 
burning  of  lamps,  the  fumes  and  smoke  from  explosives,  and 
the  noxious  and  inflammable  gases  given  off  from  the  coal 
and  surrounding  rocks,  which  make  it  essential  that  adequate 
ventilation  should  be  provided. 

Various  means  of  producing  ventilation  in  mines  have 
been  employed  in  the  past.  The  furnace,  the  water-fall, 
the  steam  jet,  and  the  displacement  machine, — similar  in 
principle  to  the  ordinary  water  pump — have  all  been  used, 
but  have  now  given  place  to  the  fan  in  a  great  majority  of 
cases. 

In  recent  years  great  alterations  have  taken  place  in  the 
design  of  mine  fans,  and  to-day  instead  of  large  and  heavy 
fans — 30  to  50  feet  in  diameter — requiring  expensive  foun- 
dations and  large  engines,  smaller  fans  running  at  higher 
speeds  are  used. 

Formerly  the  blades  of  fans  extended  from  the  centre  to 
the  circumference  and  were  straight  or  curved  backwards  in 
the  opposite  direction  to  that  of  rotation. 


56  An  Introduction  to  Mining  Science. 

Now  the  tendency  is  to  make  the  blades  very  short  leav- 


FIG.  29. — Fan  with  short  blades  curved  forwards. 

ing  the  centre  of  the  fan  clear,  and  they  are  often  curved 
forward  in  the  direction  of  rotation  of  the  fan. 


FIG.  30. — Fan  with  long  blades  curved  backwards. 
In  order  to  efficiently  ventilate  a  large  modern   mine 


Air  Currents  and  how  they  are  Caused.        $7 

enormous  volumes  of  air  are  required,  and  very  powerful 
engines  are  necessary  to  drive  the  fan.  A  quantity  of 
300,000  cubic  feet  per  minute  is  not  unusual,  and  assuming 
a  cubic  foot  of  air  to  weigh  ij  oz.  we  find  that  about  10 
tons  of  air  goes  down  the  pit  every  minute,  or  about  15,000 
tons  every  twenty-four  hours.  The  reason  why  such  power- 
ful engines  are  required  to  drive  the  fan  is  that  the  air  in 


1 


i  i 


-- J  i 


L ' 


1 


FIG.  31. — Plan  showing  method  of  ventilating  a  mine  by  a  continuous 
current  of  air. 

D,  U,  Downcast  and  upcast  shafts.  D,  Doors  in  roadways. 

passing  through  the  roadways  meets  with  so  much  resistance 
from  the  roof,  sides,  and  floor.  The  smaller  the  airway 
the  greater  is  this  resistance,  so  that  for  efficient  and  econ- 
omical ventilation  large  airways,  as  square  in  section  as 
possible,  are  advisable. 

In  the  early  days  of  mining  it  was  the  custom  to  send  the 
air  round  the  mine  in  one  long  continuous  current,  but  now 
it  is  split  up  into  a  number  of  shorter  currents  each  ventilat- 
ing a  separate  district.  In  this  way  the  men  get  fresher  air  ; 


58  An  Introduction  to  Mining  Science. 

an  outburst  of  gas  in  one  district  does  not  necessarily  foul 
the  air  in  another  district ;  the  quantity  of  air  going  into  the 
mine  is  increased  and  the  ventilation  is  more  efficient  in 
every  way.  In  order  to  make  the  air  travel  in  the  path  de- 
cided upon  and  to  ensure  that  each  district  shall  receive  its 
proper  share  of  the  ventilation,  air  crossings,  doors,  sheets, 
and  regulators  are  necessary. 


FIG.  32. — Plan  showing  method  of  splitting  the  air  current. 
D,  U,  Downcast  and  upcast  shafts.         D,  Doors  in  roadways. 

In  some  cases  an  airway  carrying  air  from  the  workings  is 
required  to  pass  over  or  under  an  airway  carrying  fresh  air 
to  the  workings,  the  angle  of  crossing  being  approximately 
at  right  angles.  The  crossing  may  be  effected  by  driving  a 
tunnel  or  stone  drift  in  the  solid  rock  over  the  road  to  be 
crossed,  or  roof  may  be  taken  down  and  an  air  crossing  of 
brickwork,  girders,  and  concrete,  or  brickwork  and  timber, 
erected. 

Doors  are  used  for  guiding  the  air  into  its  proper  path 
and  to  prevent  it  taking  a  short  cut  back  to  the  upcast 


Air  Currents  and  how  they  are  Caused. 


59 


shaft.  They  are  made  of  wood  and  hang  on  a  wooden 
frame  fixed  in  the  roadway,  the  spaces  between  the  frame 
and  the  sides  of  the  roadway  being  filled  in  with  bricks  and 
mortar. 

Sheets  or  canvas  doors  are  used  for  the  same  purpose  as 


FIG.  33. — Photograph  of  model  of  an  air-crossing.  Girders  are  placed 
across  brick  walls  the  space  between  them  being  filled  in  with 
concrete.  Double  brick  walls  are  built  on  the  girders  and  the 
spaces  between  them  filled  in  with  stone  packing. 

doors  in  less  important  positions.  They  are  often  made  of 
a  kind  of  tarred  canvas  called  brattice  cloth  and  hung  from 
suitable  supports  near  the  roof. 

At  Leycett  Colliery  in  North  Staffordshire  sheets  of 
leather  are  used.  The  leather  is  fastened  with  a  clip  made 
of  two  strips  of  wood  which  is  attached  to  a  strong  lath  by 
means  of  a  number  of  hinges  ;  this  lath,  fastened  near  the 


60  An  Introduction  to  Mining  Science. 


•J*-^- 


•M- 


-«'-0" 

-3'-nf 


FIG.  34. — Drawing  giving  particulars  of  leather  ventilating  sheet. 


FIG.  35. — Photograph  of  ventilation  door. 


Air  Currents  and  how  they  are  Caused.         6 1 

roof,  supports  the  sheet.  The  leather  being  much  stronger 
than  canvas  does  not  wear  away  so  quickly,  and  it  also 
answers  better  the  purpose  for  which  it  is  intended. 

When  the  various  districts  into  which  the  air  is  split  are 
unequal  in  length,  the  shorter  splits  would  get  more  than 
their  proper  share  of  air  unless  means  were  adopted  to 
prevent  this. 

The  regulator  by  reducing  the  area  of  the  roadway  in  the 
shorter  splits  regulates  the  quantity  of  air  passing  in  the 
various  splits  and  ensures  the  proper  quantity  going  into 
each. 

When   the  use  of  roadways  connecting  the  intake  and 


FIG.  36. — Photograph  of  regulator  (door  closed). 

return  airways  of  a  mine  is  discontinued,  these  roadways 
must  be  sealed  up  by  stoppings  which  should  be  built  to 
specifications  laid  down  in  Regulations  under  the  Coal 
Mines  Act. 

It  is  often  necessary  to  drive  headings  or  roadways  into 
the  solid  coal.  These  are  usually  driven  in  pairs  and  are 
connected  at  intervals  by  cross  roads  or  slits.  Ventilation 
is  carried  to  the  face  of  these  headings  usually  by  means  of 
brattice  cloth  or  air  pipes  (see  Fig.  37,  p.  62,  Nos.  i  and  2). 

No.  i  shows  the  method  of  ventilating  a  pair  of  headings 
under  normal  working  conditions.  No.  2  shows  method  of  re- 
moving an  accumulation  of  fire-damp  from  a  pair  of  headings. 
The  stopping  at  A  is  taken  out  and  brattice  cloth  erected  as 


62 


An  Introduction  to  Mining  Science. 


shown  by  dotted  lines,  removing   the   gas   in   layers  or  slices 
until  B  is  reached.     The  stopping  B  is  then  taken  out  and  a 


Gas 


Gas_ 


iW 


FIG.   37. — Showing  method  of  ventilating  headings  and  method   of 
removing  fire-damp. 

similar   method  of  procedure  adopted    until   the  whole  of  the 
headings  are  clear  of  gas. 

It  is  very  important  that  the  quantity  of  air  passing 
into  the  various  districts  of  a  mine  should  be  known. 
Quantity  in  the  case  of  mine  air  is  usually  expressed  in 
cubic  feet  per  minute,  and  the  product  of  the  speed  in  feet 
per  minute  and  the  area  of  the  roadway  in  square  feet  will 
give  this  result. 

The  speed  of  the  air  current  may  be  obtained  by  causing 
smoke  or  dust  to  travel  in  the  air  and  then  measuring  the 


Air  Currents  and  how  they  are  Caused.        63 

time  taken  for  this  smoke  or  dust  to  travel  a  measured 
distance. 

Example:  Smoke  travels  25   yards  in   13  seconds,  find 
speed  in  feet  per  minute. 
25  yards  =75  feet. 

—  =  feet  travelled  in  i  second 
*3 

7=1  x  60 

-£ —  ==  feet  travelled  in  i  minute 

13 

=  346  feet  per  minute  (approx.). 

The  smoke  necessary  for  measuring  the  speed  of  the  air 
current  may  be  made  by  lighting  a  very  small  quantity  of 
gunpowder  or  a  piece  of  powder  fuse,  but  this  method  is 
only  suitable  for  mines  where  inflammable  gas  is  unknown 
and  which  are  worked  by  naked  lights.  In  gassy  mines  the 
fumes  formed  by  bringing  together  ammonia  and  hydro- 
chloric acid  might  be  used,  and  a  rough  measurement  could 
be  obtained  by  throwing  a  handful  of  fine  dust  into  the  air. 

The  above  method  if  carefully  done  is  very  accurate  t  and 
very  useful  for  checking  purposes,  but  in  practice  a  special 
instrument  called  an  anemometer  (see  Fig.  38)  is  used.  It 
consists  of  a  number  of  vanes  placed  obliquely  round  an 
axis.  The  air  blowing  into  the  vanes  turns  the  axis,  which 
motion  is  communicated  by  suitable  mechanism  to  dials 
which  register  the  number  of  feet  of  air  passing. 

To  measure  the  air  the  reading  of  the  instrument  is 
first  taken.  It  is  then  held  in  the  airway  for  a  given  time, 
say  one  minute,  and  a  second  reading  taken. 

The  difference  in  the  two  readings  will  then  give  the 
speed  in  feet  per  minute. 

The  following  extracts  from  Regulations  under  the  Coal 
Mines  Act,  1911,  are  very  important  and  should  be  im- 
pressed upon  all  mine  workers  : — 

"  i.  If  any  person  shall  cause  or  become  aware  of  any 
obstruction  in  or  interference  with  the  ventilation  he  shall  if 
it  falls  within  the  scope  of  his  duties  to  remedy  such  obstruc- 
tion, interference,  or  other  source  of  danger,  immediately 
take  the  steps  necessary  for  the  purpose,  and  if  not  he  shall 
immediately  inform  the  manager,  under- manager,  deputy,  or 


64 


An  Introduction  to  Mining  Science. 


other  official,  and  shall  if  he  is  working  at  the  place  where 
the  danger  exists  cease  all  work  at  that  place. 

"2.  No  person  shall,  without  authority,  pass  beyond 
any  fence  or  danger  signal  or  open  any  locked  door. 

"  3.  Every  workman  working  at  the  face  shall  to  the  best 


FIG.  38. — Anemometer. 

of  his  power  carry  on  his  work  so  as  at  all  times  to  leave  a 
free  passage  for  the  air  current. 

"4.  Every  person  having  occasion  to  pass  through  any 
door  or  canvas  screen  or  flap  shall  carefully  close  the 
same." 

QUESTIONS. 

1.  How  is  the  air  in  underground  workings  of  mines  fouled  ? 

2.  What  dangers  are  likely  to  arise  from  the  breathing  of  impure 
air  ?     Consult  your  history  book  on  the  story  of  the  Black  Hole  of 
Calcutta  before  answering  the  question. 


Air  Currents  and  how  they  are  Caused.         65 

3.  A  large  colliery  may  be  circulating  500,000  cubic  feet  of  air  per 
minute.     Why  should  such  a  large  quantity  be  used  ? 

4.  What  agency  is  continually  pressing  air  forward  in  your  mine 
from  the  downcast  to  the  upcast  shaft  ? 

5.  What  are  the  advantages  of  splitting  the  intake  air  into  several 
different  currents  instead  of  making  it  one  big  current  passing  through 
all  the  working  places  ? 

6.  Entering  a  public  building   by  the  main  door  which  opens  to 
three  main  corridors  on  the  ground  floor  a  strong  wind  is  blowing. 

Explain  why  in  a  narrow  way  off  one   main  corridor  very  little 
movement  of  air  is  felt. 

7.  At  a  certain  colliery  the  fan  pulls  250,000  cubic  feet  of  air  per 
minute  through  the  mine  and  the  return  air  shows  the  presence  of 
i  per  cent  of  gas. 

Find  the  volume  of  "  gas  "  in  cubic  feet  the  fan  clears  out  per  day 
of  24  hours. 

8.  If  the    above  gas  could  be   collected  by  itself  and   used   in    a 
batswing  burner  consuming  4  cubic  feet  of  gas  per  hour,  find  how  long 
it  would  last. 

9.  As  the  working  of  coal  gives  rise  to  the  liberation  of  much  gas, 
do  you  think  that  the  ventilation  should  alter  with  the  output  of  coal  ? 
Give  reasons. 

10.  Ventilation   if  good   is  said   to  be  the   most  important  of  all 
things  in  making  for  safety  in  the  mine.     What  does  this  statement 
mean  ? 

11.  Is  the  use  of  a  good  safety  lamp  more  important  to  the  safety 
of  the  mine  than  good  ventilation  ? 

12.  An   office  fan  consists  of  a  wheel   of  4  vanes,  is  driven  by 
electricity,  and  when  running  draws  a  current  of  air  through  a  room. 
Explain  why  the  lower  free  ends  of  maps  and  almanacs  hanging  on 
a  wall  are  drawn  away. 

13.  Explain  why  a  lighted  candle  has  its  flame  pulled  towards  a 
revolving  fan,  and  if  brought  too  near  is  extinguished. 

14.  What  advantages  are  to  be  gained  by  replacing  the  atmosphere 
of  the  mine  by  fresh  air  ?     Why  is  mine  air  likely  to  be  unhealthy  if 
not  diluted  with  fresh  air  ? 

15.  The  standard  of  purity  for  mine  air  is  not  less  than  19  per  cent 
oxygen  and  not  more  than  i^  per  cent  of  carbon  dioxide.     State  the 
differences  between  these  amounts  and  those  found  in  fresh  air.    Why 
should  the  standard  only  apply  to  oxygen  and  carbon  dioxide  ? 

16.  Explain  how  a  street  lamp,  not  an  electric  one,  is  ventilated, 
i.e.  the   manner  in  which  it  gets  fresh    air   and  gets  rid  of  foul  air. 
Does  an  electric  lamp  require  ventilation  ? 

17.  An  individual  breathes  about  400  cubic  feet  of  air  in  twenty- 
four  hours.     Count  the  number  of  breaths  you  make  in  a  minute 
(generally  it  is  about  eighteen),  and  then  calculate  the  number  of  cubic 
inches  of  air  you  take  in  at  each  breath. 

18.  What  has  the  air  gained  and  lost  as  a  result  of  your  breathing  it  ? 

19.  What  is  the  intake  for  fresh  air  in  your  bedroom,  living  room, 
and  schoolroom  ?    Is  there  anything  similar  to  an  upcast  shaft  ?    Give 
in  each  case  the  return  airways. 

5 


66  An  Introduction  to  Mining  Science. 

20.  George  Stephenson  as  far  back  as  1835  said  that  in  order  to 
avoid  explosions  in  mines  two  shafts  should  always  be  sunk.     What 
advantages  are  there  in  two  shafts  for  ventilation  purposes  ? 

21.  Explain  why  convection  currents  are  produced  around  every 
source  of  heat.     Are  these  currents  produced  by  a  filament  electric 
lamp  ? 

22.  What   is   the   value  of  convection   currents   in   ventilating  a 
room  ?     A  coal  fire  requires  3^  times  more  air  for  combustion  than  a 
gas   stove   fire.      Which    do   you   therefore   consider  the  better   for 
ventilating  a  room  ? 

23.  A  watchman's  fire,  red  hot  in  daylight,  showed  flickering  of  the 
air  around  it.     Explain  how  this  is  caused. 

24.  Consider  the  arrangement  in  the  Bunsen  burner  for  the  intake 
of  air,  and  then  explain  how  mines  might  be  ventilated  by  a  jet  of 
high-pressure  steam.    This  was  actually  done  for  the  first  time  in  1828 
at  the  bottom  of  the  upcast  shaft. 

25.  How  can  it  be  proved  that  air  has  weight  ?     Will  the  weight 
of  (i)  a  cubic  foot  of  air,  (2)  a  particle  of  air,  vary  with  its  tempera- 
ture ? 

26.  What  is  a  blower  ?     Is  the  pressure  of  the  gas  in  a  blower 
greater  than  that  of  the  air  ?     Make  a  comparison  between  the  actions 
of  a  blower  and  those  in  the  tin  can  experiment  on  the  weight  of  the 
air. 

27.  Consider  the  following  fact  and  then  answer  the  question.     A 
fall  of  i  inch  in  the  height  of  the  barometer  means  a   decrease  of 
weight  of  the  air  on  every  square  inch  of  surface  in  the  mine  of  2  Ib. 
If  there  is  such  a  fall  in  the  barometer  on  any  day,  is  gas  in  the  gob  or 
waste  likely  to  escape  more  easily  ? 

28.  Consider  the  following  figures  : — 

1000  cubic  feet  of  air  at    32°  F.  weigh  81  Ib. 
„      „  110°  F.       „      70  Ib. 

If  a  ventilating  fan  pulls  through  a  mine  250,000  cubic  feet  of  air  per 
minute,  will  its  weight  vary  in  summer  and  winter  ? 

29.  Can  you  explain  why  a  cubic  foot  of  air  should  have  a  less 
weight  at  a  high  temperature  than  at  a  low  one  ? 


CHAPTER  IV. 

THE  INCREASE  IN  SIZE  OF  SUBSTANCES  BY  HEAT, 
AND  ITS    USEFUL  APPLICATIONS. 

ALL  bodies  possess  the  power  of  taking  up  heat,  and  as 
it  is  taken  up  the  heat  has  several  effects  upon  them ;  it 
alters  their  hotness  or  temperature ;  makes  them  increase 
their  size ;  it  may  also  make  a  body  change  from  a  solid  to 
a  liquid,  or  even  to  a  vapour. 

Experience. 

Recall  some  common  facts  to  show  that  solids,  liquids,  and 
gases  take  up  heat.  Water  contained  in  a  kettle  and  put  on  the 
fire  gets  heated.  The  solid  material  of  the  kettle  first  takes  up 
the  heat  and  then  passes  it  on  to  the  liquid  water. 

The  sun's  heat  passing  into  a  greenhouse,  or  in  any  room 
with  plenty  of  glass  windows,  heats  the  air  inside. 

The  foregoing  experience  is  common  to  all  of  us ;  it  might 
be  very  much  extended.  It  is  sufficient  to  note,  however,  that 
it  points  out  that  all  kinds  of  substances,  solid,  liquid,  and 
gas,  will  take  up  heat.  It  is  owing  to  their  temperature 
having  increased  that  we  feel  quite  sure  they  have  absorbed 
heat. 

Take  the  second  effect  caused  by  absorption  of  heat,  i.e. 
increase  in  size ;  this  has  to  be  allowed  for  in  structures 
made  of  metal. 

Experience, 

Gaps,  of  at  least  half  an  inch,  are  left  between  the  ends  of  the 
rails  on  the  railroad  ;  metal  bridges  are  constructed  with  one  end 
free  to  move  on  rollers,  e.g.  a  distance  of  6  inches  is  allowed  in  the 
Forth  Bridge  for  its  free  expansion.  Furnace  chimneys  of  brick 
have  iron  bands  around  them  to  control  their  expansion.  A  vessel, 

67  5* 


68  An  Introduction  to  Mining  Science. 

e.g.  a  saucepan,  exactly  filled  with  water  will  overflow  long  before 
it  boils.  The  liquid  in  the  thermometer  rises  in  height  as  it  takes 
up  heat. 

As  a  body  loses  heat  it  decreases  in  size ;  its  decrease  in 
size  on  cooling  will  be  exactly  the  same  amount  as  its 
increase  on  being  heated  if  it  starts  at  the  temperature  of 
the  air  and  finally  cools  to  the  same  temperature. 

Experience, 

The  wheelwright  puts  the  iron  hoop  in  a  red-hot  state  on  the 
wooden  rim  of  the  wheel.  Circular  iron  plates  are  often  seen  on 
outer  walls  of  buildings  ;  these  are  connected  inside  by  an  iron 
rod  running  from  plate  to  its  opposite  plate.  The  iron  rod  was 
screwed  up  hot  and  on  cooling  drew  up  the  leaning  walls. 

Here  we  have  the  shrinkage  of  the  cooling  metal  exerting 
a  great  force  which  is  utilized  in  tightening  the  parts  of  the 
wheel  or  pulling  in  leaning  walls. 

This  passage  back  of  a  heated  body  to  its  original  length, 
like  its  expansion,  is  not  a  jerky  process  but  a  gradual  con- 
traction ;  as  the  body  loses  equal  small  amounts  of  heat  its 
size  decreases  by  equal  small  amounts. 

Experiment, 

The  expansion  and  contraction  of  any  iron  structure  may  be 
shown  by  the  following  experiment  (Fig.  39). 

An  iron  bar  about  20  inches  long  is  supported  on  two  blocks  ; 
one  end  of  the  bar  is  put  in  contact  with  a  heavy  weight.  The 


FIG.  39. 

other  end  rests  on  a  big  pin,  or  needle,  which  is  passed  tightly 
through  a  strip  of  cardboard  as  an  indicator,  the  position  of 
this  indicator  in  front  of  a  piece  of  cardboard,  or  a  protractor,  is 
shown  in  Fig.  39.  Heat  the  bar  strongly  by  a  Bunsen  flame. 

The  expansion  of  the  bar  does  not  push  the  pin  along, 
the  latter  acting  as  a  roller   tends  to   turn   the   indicator 


The  Increase  in  Size  of  Substances  by  Heat.     69 


round.  In  this  way  the  lengthening  of  the  bar  on  heating 
is  proved.  As  the  bar  cools  it  will  contract  and  the  indicator 
will  return  to  its  original 
position.  Compare  this  ar- 
rangement with  the  practical 
arrangement  of  one  end  of 
a  bridge  being  placed  on 
rollers  to  allow  for  length- 
ening. This  experiment 
illustrates  the  plate  and  bar 
method  for  straightening 
leaning  walls  ;  after  heating 
and  screwing  up  the  plates, 
the  cooling  bar  produces  an 
irresistible  pull. 

The  following  experiment, 

based  on  using  the  ball,  a,          FlG>    a_Gravesande's  ring, 
and  the  ring,  m  (see  Fig.  40), 
will  illustrate  the  action  of  the  contracting  iron  hoop. 

Experiment. 

Notice  that  the  ball,  a,  will  only  just  pass  the  ring,  m,  when 
both  are  cold  ;  then  if  the  ring  is  heated  the  ball  will  pass 
through  easily,  and  as  the  ring  cools  it  contracts  and  the  ball 
will  again  only  just  pass  through.  The  figure  shows  the  ball 
when  it  has  been  heated,  and  owing  to  expansion  it  does  not 
pass  through  the  cool  ring. 

Solid  substances,  when  heated,  increase  in  size  by  a  very 
small  amount,  but  gases  increase  considerably.  As  the  air 
is  a  gas  it  may  be  very  conveniently  used  for  showing  expan- 
sion, but  any  other  gas  would  behave  in  precisely  the  same 
way. 

Effects  of  Heat  on  Air. 
Experiment. 

Take  a  small  flask  and  fit  (see  Fig.  41)  its  mouth  with  a 
cork  ;  through  the  latter  pass  a  well-fitting  glass  tube.  The 
tube  should  project  beyond  the  cork,  about  £  inch  inside  and 
about  8  inches  outside  the  flask.  Invert  the  apparatus  so  as  to 
put  the  tube  in  a  tumbler  of  water  ;  on  warming  the  flask  gently, 


;o 


An  Introduction  to  Mining  Science. 


e.g.  by  the  hand,  bubbles  of  air  pass  through  the  water.     Allow 


FIG.  41. — Showing  air  expands  by  the  heat  of  the  hand. 

the  flask  to  cool  in  the  position  shown  in  the  figure,  and  observe 
that  water  rises  up  the  tube. 

An  Explanation  of  the  Effects. 

The  experiment  starts  with  a  flask  of  air  which  is  of  the 
same  density  as  the  atmosphere,  that  is,  the  weight  of  a  cubic 
inch  of  air  inside  the  flask  is  the  same  as  the  weight  of  a 
cubic  inch  outside.  When  the  air  in  the  flask  is  heated  it 
increases  in  bulk;  the  bubbles  coming  out  show  there  is 
an  increase.  It  follows  then  that  there  is  after  heating  less 
weight  of  air  in  the  flask,  and  therefore  its  density,  i.e.  its 
weight  per  cubic  inch,  has  decreased.  As  the  air  in  the 
flask  cools  it  shrinks  to  its  original  density,  and  stops 
shrinking  when,  as  at  the  beginning,  the  inside  and  outside 
air  is  again  equal  in  density. 

Heated  air,  therefore,  is  lighter  than  cool  air,  but  it  may 
lose  its  heat  and  so  come  back  to  its  original  state.  Cool 
air  by  its  greater  weight  can  push  lighter  air  out  of  its 
place. 


The  Increase  in  Size  of  Substances  by  Heat.     71 

The  meaning  of  the  word  density  is  of  some  importance 
and  should  therefore  be  grasped.  If  a  liquid,  or  a  solid,  or 
a  gas,  be  heated  and  it  increases  in  volume  its  density  must 
get  less.  Consider  the  following  three  substances  and  their 
weights  per  cubic  foot : — 

Air         .         .         .         .  -08  Ib. 

Water    .         '.  .       62-50  Ib. 

Iron       ....     46875  Ib. 

When  heated  they  all  increase  in  bulk  and  so  their  weight 
per  cubic  inch  or  cubic  foot  must  decrease.  This  means 
that  there  will  be  fewer  particles  in  a  cubic  inch  or  cubic 
foot,  and  so  the  density  has  decreased.  If  i  cubic  foot  of 
air  had  the  temperature  of  ice  and  were  then  heated  to  a 
temperature  2|  times  as  great  as  that  of  boiling  water  it 
would  become  2  cubic  feet  and  its  weight  per  cubic  foot  be 
•04  Ib.  It  follows  then  the  particles  per  cubic  foot  have 
been  halved  in  number,  and  therefore  it  is  said  the  density 
has  been  halved. 

Illustration. 

The  numbers  and  words  on  this  page  are  3 1 7  and  the  size  of  the 
page  317  sq.  inches  ;  therefore  it  may  be  said  that  their  density 
is  10  per  sq.  inch.  If  the  numbers  and  words  were  halved  or 
doubled  the  density  would  be  5  or  20. 

The  Expansion  of  some  Common  Substances, 

If  the  following  substances  are  heated  from  the  tempera- 
ture of  melting  ice  to  the  temperature  of  boiling  water,  they 
will  increase  in  size  to  different  extents ;  the  relative 
amounts  of  increase  are  shown  by  the  following  figures : — 

Iron  ....  i 
Zinc  .  .  .  2-J- 

Mercury  ...  5 
Water  .  .  .  .12 
Air  .  .  .  .100 

The  table  points  out  the  large  amount  by  which  air.  expands 
compared  with  iron  for  the  same  rise  of  temperature  ;  it  also 
points  out  another  general  fact,  that  liquids  do  not  expand 
as  much  as  gases  but  more  than  solids.  The  table  further 


72  An  Introduction  to  Mining  Science. 

shows  that  solids  and  liquids  differ  in  their  amounts  of  ex- 
pansion. The  number  representing  air  would  do  for  any 
other  gas,  e.g.  marsh  gas,  which  means  that  all  gases  expand 
by  the  same  amount  for  the  same  increase  of  temperature. 

Experiment. 

Strike  a  match,  or  light  a  taper,  and  notice  that  whatever  be 
the  position  of  the  burning  body  the  flame  is  directed  upwards. 

The  flame  is  lifted  upwards  by  two  causes  :  the  vapour 
forming  the  flame  is  lighter  than  air  and  therefore,  like  a 
balloon,  tends  to  rise ;  again  the  heat  of  the  flame  expands 
the  air  and  so  starts  rising  currents.  The  joint  effect  is  to 
pull  the  flame  upwards. 

Measuring  Temperature  by  the  Expansion  of  a  Sub- 
stance, 

If  a  body  does  not  change  in  temperature  we  are  certain 
that  it  is  neither  gaining  nor  losing  heat,  and  it  will  not  in 
such  a  condition  alter  in  either  length,  breadth,  or  thick- 
ness. We  may  regard  heat  in  its  action  on  a  body  as  be- 
having like  a  force  which  by  pushing  the  particles  of  the 
body  further  apart  increases  its  size. 

If  an  iron  rod  were  fixed  on  the  wall  of  a  room  it  would 
increase  in  length  as  the  air  of  the  room  became  hotter,  the 
increase  would  be  difficult  to  see,  or  to  show  in  a  simple 
manner  that  the  rod  had  increased  in  length.  A  solid  is 
therefore  not  a  practicable  thing  for  measuring  alterations  of 
temperature  by  observing  its  increase  of  length. 

Recall  the  experiment  on  p.  68  (Fig.  39),  and  notice  that 
you  were  not  asked  to  measure  the  increase  in  length  of 
the  bar;  such  a  measurement  would  not  have  been  an  easy 
matter.  The  bar  increases  in  length  by  a  very  small 
amount  and  only  by  special  means,  or  in  a  special  way,  can 
it  be  measured. 

An  Experiment  Described. 

The  bar  of  iron  used  in  this  experiment  was  exactly  20  inches  in 
length  ;  it  had  been  kept  in  a  cupboard  whose  temperature  was 
60°  F, ,  this  was  therefore  the  temperature  of  the  bar.  It  was 


The  Increase  in  Size  of  Substances  by  Heat.     73 


then  placed  on  two  pennies,  one  at  either  end,  resting  on  the 
stove  of  a  school-room.  On  the  upper  face  of  the  iron  was  tied, 
by  wire,  a  thermometer,  which  in  time  showed  an  unaltering 
temperature  of  260°  F.  An  attempt  was  then  made  to  measure 
the  bar's  length  by  a  2 -foot  rule  but  no  increase  of  length  could 
be  with  certainty  detected.  By  a  special  way  of  measuring  it 
was  found  to  have  increased  TV  of  an  inch  in  length. 

If  in  order  to  measure  changes  of  temperature  it  were 
suggested  to  use  a  gas  shut  up  in  a  glass  tube, 
the  difficulty   due   to   its  having    no    visible 
surface,   and  of   its  filling  the   tube,   would 
render  it  necessary  to  abandon  the  idea. 

Now  a  liquid  has  a  surface  which  can  easily 
be  seen,  and  it  may  fill  the  tube  in  which  it 
is  placed  to  any  desired  extent.  Moreover, 
the  table  on  p.  71  tells  us  that  liquids  expand 
more  than  solids,  and  therefore  any  increase 
of  height  of  a  liquid  in  a  tube  would  be  more 
easily  seen  than  the  expansion  of  a  metal  rod. 

Experiment, 

Fit  up  a  flask  as  shown  in  Fig.  42. 

A  long  fine-bore  tube  passes  through  a  cork  ; 
it  must  be  well  fitted  so  as  to  prevent  water  oozing 
through  the  joint.  Fill  the  flask  completely  with 
water,  then  when  the  cork  and  tube  are  replaced 
in  the  flask  water  will  rise  up  the  tube.  Mark 
its  position  by  a  strip  of  gummed  paper.  Warm 
the  flask  gently  by  holding  it  high  above  a  gas 
burner,  and  note  the  effect  on  the  water  in  the 
tube.  Allow  the  flask  to  cool  and  note  what 
happens  in  the  tube. 

The  surface  of  the  liquid  in  the  tube  may 
sink  as  the  flask  is  first  warmed ;  the  flask 
has  expanded,  and  its  holding  capacity  in- 
creased, before  the  water  has  had  a  chance  to 
do  so.  After  this  the  water  expands  and 
creeps  slowly  up  the  tube,  but  on  cooling 
sinks  to  its  original  level.  Similar  effects 
would  be  obtained  with  other  liquids,  e.g. 
alcohol,  turpentine,  mercury,  etc. 


FIG.  42.  — 
Flask  fitted 
ready  for 
filling  with 
water  ;  to 
show  ex- 
pansion on 
warming. 


74  An  Introduction  to  Mining  Science. 

In  principle  the  apparatus  is  a  thermometer,  and  if  its 
tube  were  marked  in  some  approved  way  it  might  be  used 
for  finding  temperatures. 

It  is  agreed  after  considering  all  the  pros  and  cons  that 
a  liquid  is  the  best  substance  for  the  purpose  of  measuring 
changes  of  temperature,  and  the  most  convenient  arrange- 
ment is  to  put  the  liquid  in  a  fine-bore  tube  sealed  at  its 
upper  end  and  a  bulb,  or  reservoir,  at  its  lower  end.  The 
reason  for  closing  the  top  is  to  keep  out  air  and  prevent 
loss  of  liquid. 

Suppose  that  such  a  tube  is  placed  in  a  room  and  it  is 
noticed  for  several  days  that  the  liquid  rises  from  the  same 
point,  travels  through  the  same  height,  and  then  falls  to  that 
same  point  again.  We  are  sure  the  temperature  in  that 
room  has  altered  by  the  same  amount  on  those  successive 
days.  Names  must  be  selected  to  denote  the  two  points 
between  which  the  liquid  has  travelled,  and  for  simplicity 
and  understanding  every  one  must  use  these  names  and  no 
others  for  these  points. 

It  is  therefore  necessary  to  come  to  some  agreement  and 
to  fix  a  starting-point  in  the  measurement  of  temperature. 
It  seems  reasonable  to  say  that  when  any  substance  has  no 
heat  in  it,  its  temperature  should  be  denoted  by  nought,  o, 
or  zero,  just  as  the  amount  of  water  in  a  dry  vessel  would 
be  represented  by  any  one  of  the  same  statements. 

Unfortunately  we  cannot  get  a  body  with  no  heat,  so  in 
fixing  the  starting-point  in  measuring  temperature  we  must 
use  a  body  which,  although  cold,  still  possesses  some  heat.  . 

Compare  this  difficulty  with  our  method  of  numbering 
years.  Nothing  is  known  of  the  beginning  of  time,  i.e.  the 
first  second  of  the  first  day  of  the  first  year  of  this  world's 
existence,  so  we  make  the  birth  of  Christ  the  starting-point, 
and  count  forward  to  the  present  year,  and  backward  for 
preceding  years,  e.g.  it  is  said  the  Pyramids  were  built  in 
Egypt  3633  years  B.C.,  i.e.  before  the  starting-point  of  the 
Christian  Era. 

The  Starting-point  on  the  Mercury  Tube. 

If  a  tube  containing  mercury  is  surrounded  by  melting 
ice  it  will  in  time  come  to  the  temperature  of  the  ice ;  as  it 


The  Increase  in  Size  of  Substances  by  Heat.     75 


does  so  the  mercury  in  the  tube  will  shrink  in  bulk  until  it 
reaches  a  certain  height,  and 
as  long  as  it  is  kept  sur- 
rounded by  melting  ice  the 
mercury  will  remain  at  this 
height.  If  the  height  of  the 
mercury  remains  unaltered, 
it  means  that  the  temperature 
of  the  melting  ice  is  always 
the  same.  Wherever  or 
whenever  melting  ice  is  got, 
then  if  a  tube  were  surrounded 
by  it  the  mercury  would  al- 
ways stand  at  the  same 
height.  This  is  a  real  start- 
ing-point, because  the  mer- 
cury never  alters  its  position  ; 
it  might  be  called  the  melt- 
ing-ice position.  It  is,  'how- 
ever, spoken  of  in  the  two 
following  ways :  Nought  de- 
grees Centigrade,  or  thirty- 
two  degrees  Fahrenheit,  and 
represented  shortly  in  these 
two  ways  :  o°  C.  and  32°  F. 


FIG.  43. — A  long,  fine,  closed 
tube  with  a  bulb  on,  placed  in 
a  test  tube  and  surrounded  by 
melting  ice. 


In  either  case  it  means  the 

same  hotness,  i.e.  the  same  temperature. 

Experience. 

A  scale  rule  is  well  known  to  you,  the  construction  of  it  for 
measuring  purposes  is  based  upon  two  fixed  points.  There  is 
one  point,  or  end,  represented  by  o,  called  the  beginning,  and 
another  end  marked  by  a  number ;  between  the  o  and  the  end 
number  there  are  many  equal  spaces.  If  we  are  considering  a 
foot  rule  then  the  end  number  is  12  and  the  spaces  between 
are  called  inches  of  length  and  represented  by  the  numbers 
lying  between  o  and  12. 

The  Second  Fixed  Point  on  the  Mercury  Tube, 

The  changing  of  ice  into  water  has  given  us  one  fixed 
point,  and  it  would  be  very  convenient  if  water  turning  to 


76 


An  Introduction  to  Mining  Science. 


steam  had  a  temperature  which  is  a  fixed  one.  It  has  been 
found  that  when  pure  water  boils  its  temperature  becomes 
fixed  and  there  is  no  further  change  as  long  as  it  is  freely 
boiling. 


C. 


FIG.  44. — The  mercury  tube  fitted 
through  a  cork  into  a  flask  con- 
taining boiling  pure  water. 


FIG.  45. — A  thermometer 
reading  both  Centigrade 
and  Fahrenheit  degrees. 


Suppose  our  mercury  tube  is  in  melting  ice  and  the  vessel 
containing  it  is  heated — usually  the  tube  is  fitted  into  a  flask 
as  shown  in  Fig.  44 — then  the  ice  changes  to  water,  and  as 
it  becomes  hotter  and  hotter  the  mercury  in  the  tube  rises 
higher  and  higher.  When  the  water  boils  the  mercury  will 
have  reached  a  certain  height  and  there  it  stops.  This 
happens  whenever  or  wherever  pure  water  is  boiled  ;  it  is  a 
second  fixed  point. 


The  Increase  in  Size  of  Substances  by  Heat.     77 

This  second  fixed  point  is  the  temperature  of  pure 
boiling  water — it  might  be  called  the  boiling-water  position. 
It  is  spoken  of  in  two  ways :  one  hundred  degrees  Centi- 
grade, or  two  hundred  and  twelve  degrees  Fahrenheit, 
written  shortly  as  100°  C.  and  212°  F.  It  must  be  remem- 
bered that  although  there  are  two  names  there  is  only  one 
temperature. 

Fig.  45  shows  file  markings  (F.F.  and  B.B.)  made  on 
the  tube  as  a  result  of  placing  it  in  melting  ice  and  boiling 
water.  It  is  plain  that  the  same  length  of  the  mercury 
column  is  represented  by  1 80  divisions,  called  degrees,  in 
one  case  and  100  in  the  other.  The  following  statement  is 
therefore  correct : — 

1 80  F.  divisions  =   100  C.  divisions. 

As  soon  as  the  tube  lying  between  the  melting-point 
of  ice  and  the  boiling-point  of  water  has  been  divided  into 
100  or  1 80  equal  divisions,  for  reading  either  Centigrade  or 
Fahrenheit  degrees  of  temperature,  the  thermometer  is 
finished. 

A  Thermometer  is  a  Graduated  Rule. 

A  comparison  between  a  rule  and  a  thermometer  will  help. 
A  scale  foot  rule  is  a  graduated  piece  of  wood  or  metal  with 
two  fixed  points  represented  by  oand  12,  and  between  these 
two  fixed  points  are  smaller  equal  divisions  called  eighths  of 
an  inch.  These  two  fixed  points  do  not  vary  in  their  distance 
from  each  other. 

A  thermometer  is  a  graduated  piece  of  glass  tubing  con- 
taining mercury  with  two  fixed  points  represented  by  o,  or 
32,  and  100,  or  212,  and  between  these  two  fixed  points  are 
smaller  equal  divisions  called  degrees.  These  two  fixed 
points  do  not  vary  in  their  distance  from  each  other  if  the 
bore  and  bulb  of  the  thermometers  are  alike. 

Centigrade  means  divided  into  hundredths,  so  in  this 
method  of  dividing  the  distance  between  melting-ice  point  and 
boiling- water  point  there  are  100  spaces.  Celsius  suggested 
this  method  of  dividing  and  numbering  the  distance,  but 
Fahrenheit,  a  Dantzig  philosopher  in  1714,  before  Celsius 
suggested  his  method,  had  divided  the  space  into  180  parts, 
starting  at  32  and  ending  at  212.  He  believed  that  o°  on 


78  An  Introduction  to  Mining  Science. 

his  scale — 3  2°  below  freezing-point — was  the  lowest  tempera- 
ture experienced  on  the  earth.  Fahrenheit's  method  is  used 
in  ordinary  daily  life  and  Celsius'  method  is  used  in  scientific 
work.  It  would  be  much  better  if  there  were  only  one 
method  for  all  purposes.  This  duplication  of  methods  of 
measuring  is  unfortunate,  but  it  is  not  confined  to  temperature 
alone. 

A  table  of  relations  between  height  of  the  mercury 
column  above  the  melting-ice  position  and  degrees  of  tem- 
perature might  be  made  as  follows  : — 

Height.  Temperatures. 

Nil o°C.    32°  F. 

One-fourth  .  .  .  .  25°  C.  77°  F. 
One-half  .  .  .  .  50°  C.  122°  F. 
Three-fourths  ...  75°  C.  167°  F. 

Full  length    ....  100°  C.  212°  F. 

Double  length         .         .          .  200°  C.  424°  F. 

Treble  length          .         .         .  300°  C.  636°^. 

Thermometers  may  be  obtained  which  are  graduated  up 
to  600°  F.  and  360°  C.  This  extension  of  graduation  to 
read  higher  temperatures  than  212°  F.  and  100°  C.  and 
lower  temperatures  than  o°  F.  and  C.  is  based  upon  adding 
divisions  on  the  stems  of  the  thermometers  with  spaces  be- 
tween them  equal  to  those  between  freezing  and  boiling- 
points. 

It  is  well  to  keep  in  mind  in  any  statements  of  temperature 
that  the  degrees  tell  us  how  much  the  substance  is  above 
or  below  the  temperature  of  melting  ice,  a  temperature  often 
reached  in  our  latitudes.  Most  common  temperatures  lie 
between  the  temperatures  at  which  water  either  changes  to 
ice  or  to  steam. 

Some  Interesting  Temperatures. 

F°.  C°. 

Bunsen  burner,  maximum         .         3400  1870 
Human  blood  heat          .             .             98*4         37 

Greatest  arctic  cold  (Amundsen)       -in  -617 

Real  zero,  no  heat  in  substance       -  459  ~273 

The  sign  -  ,  called  minus,  placed  before  a  number  re- 


The  Increase  in   Size  of  Substances  by  Heat.     79 

presenting  degrees  means  that  number  of  degrees  below 
o°  C.  or  o°  F.  Compare  1915,  the  present  year's  number, 
with  1915  B.C.;  the  sign  B.C.  must  be  added  to  signify  to 
which  of  the  two  we  refer. 

Experiment. 

Take  a  Centigrade  thermometer  which  has  been  in  the  air 
and  compare  its  reading  and  graduations  with  the  one 
shown  in  Fig.  46.     Notice    the  points  necessary   to 
answer  these   questions  : — 

(1)  Is  the  thermometer  shown  a  Centigrade  one  ? 
It  has  been  hanging  in  the  air  on  an  April  day. 

(2)  How    many  degrees    are   there   between   two 
neighbouring  marks  ? 

(3)  Would  it  be  of  any  value  for  finding  the  boil- 
ing-point of  water  ? 

(4)  What  is  the  temperature  it  reads  ? 

Underground  Temperature. 

The  temperature  of  the  rocks,  through  which 
the  shafts  of  a  mine  are  sunk,  increases  as  their 
depth  increases,  and  it  may  generally  be  said  that 
there  is  an  increase  of  i°  F.  for  each  60  feet  that 
the  shaft  goes  down.  The  temperature  below  will 
therefore  be  greater  than  it  is  on  the  surface. 

Example, 

The  ordinary  temperature  of  a  South  Yorks  Colliery 
is  said  to  be  80°  F.,  the  temperature  being  taken  by 
a  thermometer  fixed  in  the  coal.  This  particular 
colliery  is  1800  feet  deep,  which  gives  a  rise  of  30° 
F.,  due  to  the  depth,  as  the  thermometer  on  the  sur- 
face read  50°  F. 

On  a  particular  day  the   temperature  at  this    FlG     6 

colliery  at  the  surface  was  found  to  be  51°  F.,  Athermo- 
which  with  the  30°  F.  added  gives  81°  F.  for  the  meter, 
temperature  of  the  workings;  actually  it  was  80°  F.  It 
should  not  be  expected  that  the  rule  of  i°  F.  for  60  feet  of 
depth  would  always  give  the  exact  underground  temperature 
even  in  this  colliery ;  there  is  such  a  thing  as  a  local  source 
of  heat  in  a  mine. 


8o  An  Introduction  to  Mining  Science. 

In  this  particular  mine  there  was  a  section  which  showed 
in  one  day  a  temperature  of  104°  F.  In  the  same  section 
a  heading  was  found  with  a  temperature  of  176°  F.  A 
temperature  of  1 15°  F.  had  been  registered  in  the  same  mine, 
and  it  is  as  well  to  remember  that  it  is  possible  for  a  brisk 
ventilating  current  to  develop  heat,  if  not  fire.  As  a  matter 
of  fact  over  sixty  fires  have  occurred  in  this  mine  in  four  years, 
and  in  many  cases  without  smoke ;  it  is  therefore  to  be  ex- 
pected that  i°  F.  for  every  60  feet  of  depth  will  not  hold 
where  there  is  chemical  action  between  air  and  some  of  the 
material  of  the  pit.  At  places  where  there  are  no  mines 
and  no  chance  of  material  getting  heated,  a  rise  is  found 
of  i°  F.  for  about  60  feet  of  depth;  it  therefore  seems  that 
the  earth  generally  gets  hotter  as  one  gets  closer  to  its  centre. 

Practical  Application  to  Mining. 

The  thermometer  or  temperature  measurer  is  an  instru- 
ment well  known  to  those  who  work  in  mines.  The  Coal 
Mines  Act  requires  that  a  thermometer  shall  be  placed  above 
ground  in  a  conspicuous  position  near  the  entrance  to  the 
mine. 

Underground  the  thermometer  is  used  for  taking  the 
temperature  of  the  workings  and  sometimes,  by  placing  the 
instrument  in  a  hole  bored  into  the  coal  or  rock,  for  as- 
certaining the  temperature  of  the  ground. 

When  exploring  a  mine  after  an  explosion  or  fire  the 
exploring  parties  would  carry  pocket  thermometers  for 
testing  the  temperature  of  the  mine  at  various  points. 

Thermometers  are  very  useful  in  cases  of  goaf  heating 
due  to  spontaneous  combustion.  The  men  whose  business 
it  is  to  look  out  for  heatings  and  fires  carry  these  instruments 
with  them  and  take  readings  at  various  points  which  are 
recorded,  thus  giving  information  which  is  sometimes  very 
valuable. 

In  the  minutes  of  evidence  given  before  the  Departmental 
Committee  on  Spontaneous  Combustion  in  Mines  some 
interesting  accounts  of  temperature  measurements  are  given. 
At  one  colliery  in  North  Staffordshire  when  heating  is  sus- 
pected, rods  of  iron  f  inch  to  -J  inch  in  diameter  and  8  to 


The  Increase  in  Size  of  Substances  by  Heat.     8 1 

i  o  feet  long  are  thrust  into  the  goaf  packs,  left  there  for  a 
short  time  and  then  taken  out  and  examined  by  feeling  them. 
This  is  done  to  try  and  find  whether  heating  is  going  on  in  the 
pack.  At  the  same  time  that  these  observations  are  being 
taken  a  thermometer  is  brought  into  use  to  find  the  progress 
of  heating;  it  is  first  hung  at  the  coal  face  and  the  tem- 
perature taken,  then  taken  into  the  suspected  waste  or  goaf; 
the  readings  are  booked  and  kept  for  future  reference. 

Another  method  is  to  use  thermometers  inserted  in  tubes 
with  the  ends  sealed  and  pointed.  These  tubes  are  driven  into 
the  goaf  and  kept  there  for  some  time  when  they  are  taken 
out  and  the  thermometer  readings  noted. 

It  is  often  necessary  to  know  the  temperature  of  the  feed 
water  for  the  boilers,  of  the  gases  in  boiler  flues  and  chimneys, 
and  of  the  boiler  furnace. 

When  the  temperature  to  be  measured  is  very  high,  a 
special  kind  of  thermometer  called  a  pyrometer  is  used. 

In  the  British  Coal  Dust  Experiments  special  instru- 
ments were  devised  for  directly  measuring  the  temperature 
of  a  coal  dust  explosion. 

Owing  to  the  very  brief  space  of  time  taken  by  an  ex- 
plosion it  is  very  difficult  to  measure  its  temperature  directly 
by  ordinary  means,  but  by  using  special  instruments  the 
temperature  of  explosion  of  high  explosives  such  as  dyna- 
mite may  be  calculated. 

Sometimes  a  continuous  record  of  temperature  is  required 
and  instruments  are  made  which  give  this  record  in  the 
form  of  a  line  drawn  on  squared  paper. 

QUESTIONS. 

1.  The  bonnet  of  a  lamp  is  found  to  have  a  temperature  of  100°  F. 
Will  it  be  any  different  in  size  from  what  it  was  when  cold  ?      Why 
is  the  bonnet  of  a  lamp  made  of  metal  ? 

2.  Why  is  it  that  in  a  chimney  flue  there  is  an  uprush  of  air  when 
there  is  a  fire  in  the  grate,  and  very  often  a  downrush  when  there 
is  no  fire  ? 

3.  There  are  two  pokers,  one  made  of  zinc  and  the  other  of  iron. 
When  no  fire  is  in  the  grate  there  they  are  equal  in  length,  will  they 
be  of  equal  lengths  as  they  arrive  at  260°  F.  due  to  a  fire  ? 

4.  How  will  you  find  the  temperature  of  the  following  :  (a)  A  cup  of 
tea ;  (b)  the  temperature  of  your  lamp  ;  (c)  the  coal  face ;  (d)  water  in 
the  mine  ? 

Have  you  any  idea  of  what  these  temperatures  would  be  ? 

6 


82  An  Introduction  to  Mining  Science. 

5.  Explain  the  meaning  of  freezing-point  and  boiling-point;  what 
is  the  idea  implied  in  the  word  "  point"  in  each  expression  ? 

6.  What  temperatures  correspond  to  140°  C.  and  -  40°  F.  ?    Why  in 
such  classes  of  work  as  steel   bridges,  steam    pipes,    boiler    furnace 
tubes,  should  consideration  have  to  be  given   to  changes  of  tempera- 
ture ?     In  which  should  the  allowance  be  greatest  ?     What  would 
happen  if  no  allowance  were  made  ? 

7.  Do  you  think  the  holes  of  wire  gauze  become  larger  on  being 
heated  ? 

8.  A  cubic  inch  of  steam  comes  out  of  the  flask  (see  Fig.  44)  and 
passes  into  the  air ;    will  its  volume  and  density  change  ?     If  so,  ex- 
plain why. 

9.  How  many  degrees  are  there  between  any  two  consecutive  lines 
on  a  thermometer  ?     What  alteration  would  have  to  be  made  to  a 
thermometer  to  make  it  read  a  difference  in  temperature  of  ^th  of  a 
degree  ? 

10.  Suppose  you  have  a  brass  ring  through  which  just  passes  a 
tally  check.     What  experiments  would  you  perform  to  show  that  the 
tally  expands  and  contracts  on  heating  and  cooling  ?    What  effect  will 
heating  have  upon  the  size  of  the  hole  in  the  tally  ? 

11.  Keeping  in  mind  the  meaning  of  boiling-point,  what  would  you 
expect  to  be  meant  by  the  phrases  melting-point  and  ignition-point  ? 

12.  Discuss  the  value  of  the  sense  of  feeling  and  of  the  eyesight  in 
judging  the  temperature  of  a  body  ;  the  former  by  the  sensations  we 
get  on  touching  bodies  and  the  latter   by  the  colour  of  hot  bodies. 
Do  you  think  they  are  exact  enough  to  measure  temperature  ?     Are 
these  ways  more  exact  in  measuring  temperature  than  a  thermometer  ? 

13.  Do  you  think  the  density  of  the  air  in  this  room  is  uniform,  i.e. 
the  same  throughout,  when  (i)  it  is  daytime  ;  (2)  it  is  lighted  up  by 
gas  ?     Give  reasons. 


CHAPTER  V. 
THE  PRINCIPLE  OF  THE  SAFETY  LAMP. 

IT  is  necessary  to  have  a  light  in  the  pit  for  working  pur- 
poses,  and  many  have  been  the  devices  for  supplying  it. 
In  the  year  1750  Spedding  invented  his  steel  mill  to 
give  a  stream  of  luminous  sparks  as  a  safer  way  of  lighting 
than  the  tallow  candle.  Then  in  1815 — a  century  ago — 
Davy  invented  a  lamp  to  give  a  better  light  and  to  be  much 
safer,  and  about  a  century  after  that  comes  the  miner's 
electric  lamp.  The  flame  safety  lamp  is  to-day  the  most 
popular ;  it  was  originally  constructed  on  the  scientific  prin- 
ciple of  using  a  metal  gauze  to  keep  the  lamp  cool,  so  as 
not  to  ignite  any  gas  in  the  mine. 

It  is  this  scientific  principle  which  we  have  to  thoroughly 
understand,  and  its  intelligent  grasp  can  only  come  from 
experimental  knowledge  of  the  action  of  a  metal  on  heat. 

A  naked  light  in  a  mine  is  a  danger  because  there  is  often 
in  the  atmosphere  around  it  sufficient  inflammable  gas  to  be 
fired  by  the  light,  then  there  is  an  explosion.  The  problem 
is  to  devise  a  method  of  protecting  from  the  flame  of 
the  lamp  the  inflammable  gas  in  the  air  around.  This 
would  be  easy  if  we  could  shut  up  the  flame  in  a  glass  case 
and  keep  out  all  air  and  gas,  but  a  flame  must  have  a  supply 
of  air  for  its  continual  burning.  It  must  also  have  a  case 
that  will  let  out  the  impurities  produced  by  the  lamp  flame. 

The  difficulty  is  therefore  how  to  give  the  lamp  a  good 
supply  of  air,  how  to  let  out  the  impurities,  and  yet  at  the 
same  time  to  keep  inside  the  lamp  the  flame  of  any  gas 
which  has  got  inside  and  become  lighted  by  the  lamp 
flame.  A  flame  surrounded  by  a  gauze  would  let  pure  air 
in  and  foul  out,  but  it  would  also  let  gas  and  coal  dust  into 
the  lamp.  Would  the  gauze  have  any  power  of  shutting  off 
from  the  outside  air  flame  produced  by  gas  burning  in- 
side the  gauze  ?  Davy  showed  experimentally  that  it  could 

83  6* 


84  An  Introduction  to  Mining  Science. 

be  relied  upon  to  do  so  to  a  certain  extent.  If  you  look  at  one 
of  the  first  lamps  made  by  Stephenson  or  Davy  (see  p.  99), 
you  will  see  the  light  is  surrounded  in  the  latter  by  a 
gauze.  At  the  present  time  the  gauze  in  a  lamp  is  not  easily 
seen,  it  has  become  two  gauzes  hidden  in  the  bonnet  of  the 
lamp ;  glass  is  now  used  for  letting  out  the  light.  These 
changes  of  structure  and  arrangement  still  leave  the  gauze 
there,  embodying  the  old  "principle  upon  which  the  safety 
lamp  was  built.  It  is  necessary  to  notice  that  in  an  oil 
safety  lamp  no  inflammable  gas  is  produced  inside  the  lamp 
and  gauze,  and  as  the  lamp  flame  is  far  from  the  gauzes  they 
cannot  become  by  its  action  very  hot.  If,  on  the  other  hand, 
inflammable  gas  and  coal  dust  pass  into  the  lamp  through 
the  gauzes,  they  may  be  ignited  by  the  lamp  flame  forming 
an  intensely  burning  mass  of  material  in  the  gauzes  of  the 
lamp ;  it  is  the  flame  of  this  that  requires  keeping  inside. 
May  its  heating  power  on  the  gauzes  in  some  way  be  de- 
creased so  that  neither  by  flame  passing  through  nor  by 
gauzes  getting  red  hot  can  the  outside  gas  be  exploded  ? 

If  the  inflammable  gas  and  coal  dust  after  getting  in  the 
lamp  can  be  burnt  without  being  dangerous  to  that  still 
outside,  then  the  gauze  achieves  a  wonderful  result.  Com- 
pare the  idea  with  that  action  of  glass,  as  used  in  greenhouses, 
by  which  heat  can  get  in  through  the  glass  but  it  cannot  as 
easily  get  out  again  ;  the  sun's  heat  is  shut  up  after  streaming 
through  the  glass. 

Experiment, 

Fix  a  short  piece  of  candle  on  to  a  small  wooden  base  (see 
Fig.  47)  and  then  make  a  cage  of  a  piece 
of  standard  wire  gauze  about  4  inches 
high  x  2  inches  diameter,  the  wooden 
base  forming  the  bottom  of  the  cage. 
Instead  of  making  a  gauze  cage  one  of 
the  gauzes  from  a  miner's  lamp  may  be 
used.  Light  the  candle  and  then  cover 
it  with  the  metallic  cage.  Take  a  Bunsen, 
turn  on  the  gas  to  a  small  extent  and 
allow  the  unburnt  gas  to  play  on  the 
FIG.  47.— Gauze  cage  e  The  gas  which  penetrates  the 

on  a  wooden  block.          gauzfi  wiu    bum    but   the    flam£    Qf   the 

burning  gas  will  not  spread  to  the  burner.     As  the  gas  is  moved 


The  Principle  of  the  Safety  Lamp.  85 

across  the  cage  slight  "  pops  "  will  be  heard,  due  to  the  ex- 
ploding gas. 

It  is  important  to  emphasize  in  this  experiment,  and  also 
in  the  general  statement  of  the  action  of  the  gauze  in  the 
miner's  lamp,  that  the  flame  of  the  gas  which  has  penetrated 
the  gauze  is  the  one  we  want  to  keep  in  bounds. 

The  keeping  inside  of  the  flame  of  the  burning  gas  in  the 
experiment  so  that  it  does  not  strike  through  and  ignite 
that  coming  from  the  burner,  is  due  to  the  cooling  action  of 
the  metallic  gauze  on  the  flame.  This  is  the  action  we  have 
to  explain.  The  experiments  following  will  therefore  be  de- 
signed to  illustrate  the  power  of  metals  to  take  heat  from 
hot  bodies  and  so  keep  their  surroundings  cool ;  this  is  the 
secret  of  the  power  of  gauze  to  confine  a  burning  mass 
of  gas. 

There  will  in  the  foregoing  experiment  be  a  heated  cur- 
rent of  air  rising  up  from  the  gauze ;  it  is  pushed  up  by  the 
cold  air  underneath  which  of  course  takes  its  place  and  gets 
heated.  This  uprush  of  air  currents  robs  the  cage  of  its  heat 
and  so  helps  in  the  cooling  process.  In  the  miner's  lamp 
there  is  an  uprushing  current,  and  this  must  help  to  cool 
the  bonnet,  and  in  its  turn  the  gauzes.  Some  of  the 
experiments  will  show  how,  by  air  rising  up  and  carrying  heat 
away,  parts  of  the  miner's  lamp  will  be  helped  to  keep  cool, 
despite  the  fact  that  the  lamp  flame  is  always  producing  heat 
as  well  as  light. 

Moving  Air  carries  away  Heat, 

A  burning  mass  of  gas  or  vapour  may  be  extinguished  in 
two  ways :  (i)  by  lowering  its  temperature  (2)  by  cutting  off 
its  air  supply,  both  of  which  may  be  of  value  in  keeping  the 
burning  in  its  place. 

Experience. 

The  familiar  way  of  "  blowing  out  the  candle  "  consists  of 
lowering  the  temperature  of  the  flame  by  a  current  of  breath  ;  in 
this  way  sufficient  heat  is  removed  from  the  flame  to  cool  it  to  a 
temperature  at  which  it  cannot  burn.  The  cooled  vapours  may 
often  be  seen  and  smelt  immediately  after  blowing  out  the  candle. 

The  blowing  out  of  all  flames,  match,  candle,  or  gas, 
is  brought  about  by  establishing  a  current  of  air  and  S.Q 


86  An  Introduction  to  Mining  Science, 

robbing  them  of  heat.  Each  flame  is  reduced  to  such  a 
low  temperature  that  it  cannot  ignite  the  fresh  vapour  or 
gas  which  feeds  it  and  so  comes  to  an  end. 

The  foregoing  piece  of  experience  is  important  to  our 
present  chapter.  The  cutting  off  of  the  air  supply  is  of 
less  importance,  it  is  fully  dealt  with  in  Chapter  II. 

Experiment, 

Take  a  thermometer  and  blow  a  stream  of  cold  air  across  the 
bulb,  or  expose  it  to  a  wind.  Notice  the  lower  temperature  that 
it  shows  after  the  action. 

This  proves  that  as  air  passes  over  a  body  it  carries  off 
heat ;  it  happens  whether  the  body  is  a  solid,  liquid,  or  a 
gas  flame. 

Take  a  block  of  wood,  B  (Fig.  48),  place  on  it  a  big  drop  of 
water  and  then  a  thin  watch  glass  or 
thin  vessel,  C.  Place  in  the  glass 
a  small  quantity  of  carbon  disulphide, 
or  ether.  From  the  nozzle  of  a  bellows, 
N,  drive  a  current  of  air  over  the  sur- 
face of  the  liquid,  and  notice  very  quickly 
the  water  turns  to  ice  and  B  is  fixed  to  C. 


The  explanation  of  the  result  is  as 
follows :  the  liquid  in  the  glass  is  a 
FIG.  48.  very   volatile    one    and    is   therefore 

easily  carried  away  by  the  current  of  air  as  vapour,  but  to 
turn  a  liquid  into  vapour  requires  heat.  The  heat  necessary 
comes  from  the  supports  of  the  glass  one  of  which  is  water, 
and  this  declares  its  loss  of  heat  by  turning  to  ice. 

Experience. 

Liquids  and  solids  are  often  cooled  by  currents  of  air  being 
blown  across  them,  e.g.  if  a  plumber  over-heats  his  soldering- 
iron  he  will  cool  it  in  this  way.  A  similar  method  is  used  in 
cooling  tea. 

The  foregoing  experience  and  experiment  prove  that 
air  carries  away  heat  from  a  body  as  it  blows  across  its 
surface.  It  is  necessary  to  realize  that  any  hot  body  will 
produce  a  current  in  the  air  around  it  and  in  this  way  start  an 


The  Principle  of  the   Safety  Lamp.  87 

air  movement  which  will  take  away  its  heat,  and  so,  reduce 
its  temperature. 

Experience, 

The  up-draught  in  the  chimney  flue  and  the  flow  of  air  into 
a  room  are  caused  by  the  heat  of  the  fire.  This  circulation  of 
air  goes  on  as  long  as  there  is  a  fire  ;  it  cannot  be  stopped  if  the 
fire  continues.  The  draught  carries  a  great  deal  of  the  heat  of 
the  fire  with  it. 

These  currents  of  air  caused  by  a  hot  body  which  carry 
away  its  heat  are  shortly  spoken  of  as  "convection 
currents  ".  The  air  is  the  vehicle  or  conveyance  by  which 
the  heat  is  carried  away,  and  so  the  phrase  is  a  good  one ; 
it  suggests  to  the  mind  actually  what  happens. 

Air  rushing  up  round  a  flame  cools  it,  lowering  its  lumin- 
osity and  temperature ;  this  effect  has  caused  the  production 
of  a  patent  gas  burner  which  heats  the  air  feeding  the  flame, 
so  as  not  to  destroy  any  of  its  luminosity. 

In  some  lamps  for  miners,  under  the  bonnet  which  has 
intake  holes  for  air,  there  is  an  inside  shield.  The  air  passes 
through  these  holes,  strikes  the  hot  shield  and  arrives  at 
the  flame  well  warmed;  the  flame  is  therefore  fed  with 
warm  air. 

Removing  Heat  by  a  Metal. 

The  cooling  of  flame  whether  produced  by  carrying  off 
its  heat  by  blowing  over  it,  or 
by  a  metal  in  contact  with  it, 
will  result  in  the  diminution  of 
its  brightness,  and  in  a  more  or 
less  pronounced  tendency  to 
smoke. 


Experiment, 

Obtain  an   iron  weight,  or  a 
laundering  iron,  and  bring  one 

of  its  faces  close  against  the  face      FIG  A   iece  of  metal 

of  a  flat  flame  ;  its  luminosity  will        ing  ],eat  awFay  from  a  flame- 
almost  disappear.    The  presence 
of  soot  and  moisture  on  the  iron  should  be  noticed. 


88  An  Introduction  to  Mining  Science. 

The  flame  gives  some  of  its  heat  up  to  the  iron,  the  latter 
being  a  metal  which  readily  takes  heat  away.  The  heat  neces- 
sary for  making  the  soot  particles  highly  incandescent  is  thus 
lost  to  the  flame,  and  so  instead  of  their  burning  away  to  an 
invisible  gas  they  collect  on  the  face  of  the  iron. 

Experience. 

A  very  similar  deposit  of  soot  is  often  seen  at  the  back  of 
the  fire-grate  where  it  forms  as  a  thin  hard  cake.  It  may  finally 
take  fire,  appearing  on  the  back  as  smouldering  lines  of  fire. 

The  cause  of  the  deposit  is  due  to  the  cooling  of  the 
flame  of  the  burning  coal ;  the  cool  air  flowing  in  above 
the  fire  keeping  the  upper  part  of  the  fire-grate  back  fairly 
cool. 

The  deposit  of  black  substance  found  on  the  gauze  of  a 
lamp  which  is  not  kept  clean  is  caused  by  too  high  a  flame, 
which  striking  the  gauze  is  cooled,  and  so  soot  particles 
are  deposited.  « 

Experiment, 

Take  some  copper  wire  about  ^  inch  in  diameter  and  coil  it 
round  a  lead  pencil,  making  it  into  a  spiral  of  about 
eight  turns.  Leave  a  piece  as  a  handle  (see  Fig. 
50).  Take  a  candle  burning  with  a  short  clean 
wick  and  bring  down  the  spiral  quickly  on  the 
flame.  The  candle  will  be  extinguished.  Bring 
the  spiral  to  a  red-hot  state  by  heating  it  in  a 
Bunsen  flame,  repeat  the  experiment,  and  notice 
FIG.  50.  —  any  different  result. 

Leading         Repeat  the  experiment  with  a  spirit  lamp  flame. 

heat      away 

b^^^^r  The  exPlanation  of  these  occurrences  is  not 
spiral ;  the  difficult.  If  a  flame  is  to  be  kept  burning  it 
candle  is  must  be  kept  hot;  it  requires  to  be  kept  at  a 

block0"  0*  high  temPerature-  The  flame  keeps  itself 
w  <°o  d  burning  by  the  heat  it  produces,  but  the  intro- 

duction of  the  copper  spiral  robs  the  flame  of 
its  heat,  and  so  it  is  extinguished.  When  the  spiral  is  made 
red  hot,  previous  to  its  surrounding  the  flame,  there  is  no 
extinction  of  the  latter.  The  student  should  notice  that  the 
spiral  does  not  extinguish  the  Bunsen  flame  when  he  is 


The  Principle  of  the  Safety  Lamp.  89 

making  it  red  hot ;  in  this  case  the  spiral  is  not  large  enough 
to  rob  the  flame  of  sufficient  heat. 

The  spiral  only  touches  the  outside  of  the  flame,  but  it 
conveys  heat  away  so  rapidly  that  the  whole  of  the  flame 
gets  cooled.  It  therefore  seems  that  a  metal  cage,  such  as 
the  spiral  is,  robs  the  flame  of  so  much  heat  that  it  is 
extinguished. 

The  experiment  suggests  that  if  a  flame  were  inside  a  cage 
made  of  metallic  gauze  and  it  came  into  contact  with  the 
gauze  the  flame  might  be  so  reduced  in  temperature  that  it 
would  be  extinguished,  or  at  least  where  the  flame  and  the 
gauze  met  there  would  be  such  a  cooling  of  the  flame  that 
as  flame  it  would  not  get  through  the  gauze. 

Experiment, 

Take  a  thermometer  and  read  its  temperature,  then  lay  the 
bulb  of  the  thermometer  on  a  flat  iron,  read  the  temperature 
again,  and  notice  any  difference  in  the  two  readings. 

Experience  and  experiment  teach  that  a  cold  solid, 
particularly  a  metal,  may  rob  a  hot  body  of  its  heat. 

Experience, 

Most  people  who  have  had  to  make  a  fire  quickly  in  the 
ordinary  fire-grate  and  have  placed  pieces  of  coal  on  the  fire 
previously  to  the  wood  getting  well  lighted  have  found  that  the 
burning  wood  is  often  put  out. 

The  coal  robs  the  flame  of  the  wood  of  so  much  heat  that 
continued  burning  is  impossible. 

Experience, 

It  is  well  known  that  if  a  poker  is  left  in  a  fire  for  a  length  of 
time  the  handle  becomes  hot. 

In  this  case  the  heat  has  passed  along  the  poker,  and  as 
a  poker  is  made  of  metal  it  follows  that  a  metal  will  take 
away  heat  from  the  fire,  allowing  heat  to  flow  continually 
from  the  end  in  the  fire  to  the  handle  in  the  air. 

The  next  experiment  will  teach  us  that  metals  differ  in 
the  ease  with  which  they  allow  heat  to  flow  through  them. 


go  An  Introduction  to  Mining  Science. 

Experiment. 

Take  two  pieces  of  wire,  one  copper  and  one  iron,  A  inch 
thick  and  6  inches  long,  and  beat  each  out  flat  at  one  end.  Place 
the  wires  on  a  support  and  clamp  the  latter  on  to  a  retort  stand, 
at  a  height  so  that  the  circular  ends  may  be  placed  in  a  Bunsen 
flame  in  equal  conditions  (see  Fig.  51).  Place  a  small  piece  of 
phosphorus,  or  a  match-head,  on  the  beaten-out  ends.  Take 
the  time  required  for  each  piece  of  phosphorus  to  ignite.  Or 
pass  a  match-head  slowly  along  the  wires  towards  the  flame  ; 
notice  the  distance  from  the  flame  where  each  match  ignites. 


FIG.  51. — Comparing  the  power  of  leading  away  heat :  arrangement 
of  the  two  wires,  or  rods,  in  the  hot  part  of  the  flame  equally. 

Phosphorus  will  ignite  always  at  the  same  temperature, 
and  the  temperature  at  which  a  match  ignites  will  be  the 
same  for  any  match  taken  from  the  same  box.  If  therefore 
the  copper  wire  ignites  the  match  at  a  greater  distance  from 
the  flame  than  the  iron  wire  does,  it  means  that  its 
temperature  is  higher  at  a  greater  distance  than  along  the 
iron  wire.  The  experiment  shows  that  heat  travels  along 
the  copper  and  goes  further  than  it  does  along  the  iron  ; 
therefore  the  copper  is  said  to  be  a  better  conductor  of  heat. 

In  a  well-arranged  and  carefully  managed  experiment  it 
can  be  shown  that  copper  is  4*8  times  better  for  conduct- 
ing heat  than  iron.  As  copper  and  iron  are  used  in  the 
making  of  lamp  gauzes  the  experiment  should  be  interest- 
ing to  us.  Kettles  are  made  of  these  two  metals,  and  it  is 


The  Principle  of  the  Safety  Lamp.  91 

a  well-known  fact  that,  for  boiling  water,  a  copper  kettle  is 
more  economical  in  the  consumption  of  gas  than  an  iron  one. 
The  experiment  might  be  used  to  show  that  any  two 
metals  differ  in  the  ease  with  which  they  allow  heat  to  flow 
along  them.  The  following  figures  show  that  this  difference 
in  conducting  heat  extends  to  other  things : — 

Air  .  .        i  Iron  .  .  4,000 

Paper  .  .        2  Zinc  .  .  5,600 

Wood  .  .6  Brass  .  .  6,000 

Glass  .  .10  Aluminium  .  6,800 

Water  .  .     40  Copper  .  .  19,200 

Sand  .  .     50  Silver  .  .  20,000 

Stone  .  .120 

As  an  example  of  the  use  and  meaning  of  these  figures, 
we  may  say  water  is  forty  times  a  better  conductor  (and  silver 
twenty  thousand  times  better)  than  air,  and  iron  a  hundred 
times  better  than  water. 

There  are  several  metals  used  in  the  construction  of  miner's 
lamps.  Aluminium  is  used  on  account  of  its  lightness, 
and  it  is  a  good  conductor  of  heat.  Brass,  which  is  a 
metal  made  of  copper  and  zinc,  is  very  largely  used ;  it  is  a 
good  conductor  of  heat. 

Bonnets  are  made  of  steel  (a  strong  variety  of  iron)  or 
aluminium.  Some  lamps  have  a  galvanized  steel  case,  i.e. 
steel  plated  with  zinc. 

We  have  all  noticed  when  metallic  bodies  are  grasped  by 
the  hand  they  give  a  sensation  of  cold,  whereas  wooden, 
cardboard,  or  cloth  bodies  do  not.  A  lamp-post  in  the 
open  air  seems  to  have  a  lower  temperature  than  a  telegraph- 
post  close  by,  but  they  are  both  at  the  same  temperature  on 
account  of  being  in  the  same  air. 

The  explanation  of  the  foregoing  facts  is  that  the  heat  of 
that  part  of  the  hand  grasping  the  thing  made  of  metal  is 
led  away,  and  although  a  fresh  supply  of  heat  comes  to  that 
part  of  the  hand  from  the  blood  it  is  also  led  away.  The 
hand  therefore  having  its  heat  constantly  taken  away  feels 
cool ;  to  accomplish  this  the  metal  must  allow  heat  to  travel 
quickly  along  it;  in  short,  it  is  a  conductor. 


92  An  Introduction  to  Mining  Science. 

Action  of  Gauze  on  Flame, 
Experiment, 

Take  a  big  beaker  or  other  wide-mouthed  vessel  and  place 
over  its  mouth  a  piece  of  copper  or  iron  gauze.  Ignite  in  a  dish 
or  spoon  a  small  quantity  of  methylated  spirit  and  pour  it  into 
the  beaker  through  the  gauze  ;  the  dish  may  be  held  by  crucible 
tongs.  As  the  spirit  passes  through  the  gauze  the  flame  will  be 
extinguished. 

If  the  burning  spirit  be  poured  through  the  air  into 
the  beaker  with  no  intervening  gauze  then  it  will  not 
be  extinguished.  The  extinguishing  action  of  the  gauze 
can  be  accounted  for  by  its  leading  off  the  heat  so 
quickly  from  the  burning  mass  that  the  temperature  is 
lowered  and  continued  burning  is  not  possible. 

Experiment, 

Take  a  Bunsen  (see  Fig.  52),  burning  with  a  non-luminous 
flame,  and  lower  a  piece  of  lamp  gauze  slowly  on  the  flame  ;  notice 
that  the  flame  does  not  pass  through  until  the  wire  gauze  gets  very 
hot.  Turn  off  the  ignited  gas  and  allow  a  stream  of  unburnt  gas 
to  play  on  the  gauze.  Try  and  light  the  gas  on  the  upper  side 
of  the  gauze,  it  will  ignite  but  the  flame  will  not  strike  through 
and  ignite  the  gas  under,  or  inside,  the  gauze  screen. 

Obtain  a  piece  of  gauze  which  has  had  some  of  its  meshes 
broken  away  and  test  its  power  to  resist  the  passage  of  flame. 


FIG.  52. — Gauze  stopping  burning  gas  from  igniting  unlit  gas  on  the 

rkr\r\r»cif^  cirf*» 


opposite  side. 

The  first  part  of  the  experiment  shows  that  the  gauze 
stops  the  flame  from  passing  through  until  it  gets  red  hot ; 
the  passing  through  is  helped  by  the  force  of  the  flame  and 


The  Principle  of  the  Safety  Lamp.  93 

the  up-draught  of  the  air.  In  a  miner's  lamp  these  two 
actions  would  not  help  in  such  a  forcible  manner,  even  when 
the  gauze  gets  red  hot  by  gas  burning  in  them. 

These  experiments  on  gauze  and  Bunsen  gas  are  intended 
to  illustrate  the  shutting  up  of  burning  gas  which  has  found 
its  way  from  the  outside  into  the  gauze  of  the  miner's  lamp, 
and  not  any  action  of  the  gauze  on  the  lamp  flame. 

It  is  important  to  notice  in  the  experiment  that  the  gauze 
breaks  up  the  flame  as  it  attempts  to  pass  the  meshes,  and 
though  the  flame,  by  its  being  flattened  slightly  covers,  say, 
3  sq.  inches  of  the  gauze,  there  are,  nevertheless,  2352  meshes, 
so  the  flame  is  split  up  into  that  number  of  parts.  These 
small  tongues  of  flame  are  well  cooled  by  the  mesh  around 
them,  on  account  of  its  good  conducting  powers  for  heat, 
and  so  cannot  get  through  ;  they  are  extinguished  in  the 
attempt.  The  uprising  current  of  air  also  carries  with  it  a 
great  deal  of  the  heat  of  the  gauze  so  helping  to  cool  the 
tongues  of  flame. 

In  the  second  part  of  the  experiment  the  flame  will  very 
seldom,  if  at  all,  strike  through  to  the  burner  underneath  ; 
the  gauze  does  not  get  hot  enough.  The  gauze  is  rapidly 
conducting  away  heat,  and  there  is  only  that  from  the  base 
of  the  flame  to  remove.  It  is  thus  very  different  from  the 
first  part  of  the  experiment  where  the  whole  of  the  flame 
helps  to  heat  the  gauze. 

The  upper  part  of  the  flame  which  is  not  in  contact  with 
the  gauze  will  have  much  of  its  heat  carried  away  by  rising 
currents  of  air. 

A  Marsaut  lamp  has  two  gauzes  (see  Fig.  53).     If  such  a 
lamp  is  available,  or  even  the 
two  gauzes  without  the  lamp, 
the      following       experiment 
should  be  performed  : — 


Experiment, 

-nT^r.  •        r    .  ^  ,  FIG.  53. — Inner  (left)  and  outer 

With  a   pair   of  tongs   take  (ri|£t)  slof  ^  j 

hold  of  the  flange  of  the  inner 

gauze  and  bring  it  down  on  to  the  flame  of  a  Bunsen  burner. 

The  gauze   will   in  time  become  hot  and  the  flame  will  pass 


94  An  Introduction  to  Mining  Science. 

through,  as  it  does  in  the  experiment  with  a  flat  gauze  (see  p. 
92).  Let  the  inner  gauze  cool  and  then  fit  it  into  its  outer 
gauze.  Now  hold  the  double  gauze  over  the  Bunsen  flame  and 
see  if  the  flame  gets  through. 

The  flame  will  probably  be  quite  unable  to  pass  through 
the  double  gauze  ;  this  is  a  real  shutting  up  of  flame.  The 
advantages  of  such  an  arrangement  in  a  fiery  mine  will  at 
once  be  seen  by  any  one  who  has  realized  how  a  flame 
may  ignite  a  gas,  and  the  lighting  of  the  house  gas  by  the 
flame  of  a  match  makes  every  one  familiar  with  it. 

The  following  details  are  helpful  in  forming  an  idea  of 
the  action  of  gauze  and  should  be  corroborated  by  measure- 
ment of  a  piece  of  standard  iron- wire  gauze.  The  Safety 
Lamps  Order  of  1913  says  every  lamp  gauze  must  have  28 
meshes  to  the  lineal  inch  (784  to  the  sq.  inch). 

Experiment, 

Measurements  of  a  piece  of  iron  gauze  6  inches  square  : — 

Lengths  of  wire  28x6x2     —  336. 

Total  length  of  wire  336  x  6  =  2016  inches,  a  little  longer 
than  two  and  a  half  times  the  length  of  a  standard  cricket  pitch, 
which  is  22  yards. 

A  length  just  wrapped  round  a  piece  of  glass  tubing  ten  times 
and  pushed  together  measured  -15  inch  in  thickness.  The  di- 
ameter of  the  wire  is  therefore  -015  inch. 

Area  of  surface  =  2016  x  3-i4  x  -015  =  94*75  sq.  inches. 

Adding  -25  for  the  area  of  the  ends  we  may  say  95  sq. 
inches. 

Weight  of  the  6-inch  piece  =  if  oz. 

Thickness  of  wire  in  a  lineal  inch  28  x  -015  =  -42  inch. 

Space  or  mesh       in  a  lineal  inch    i  -      -42  =  -58  inch. 

The  gauze  has  therefore  more  mesh  area  than  wire  area. 

The  figures  show  that  if  a  small  block  of  iron  weighing 
if  oz.,  which  will  be  about  the  size  of  a  small  strawberry,  is 
drawn  out  into  a  length  of  2016  inches,  a  surface  of  95 
sq.  inches  is  obtained— about  three  times  the  size  of  this 
page.  This  big  surface  puts  the  wire  in  a  good  position  to 
lose  the  heat  that  it  receives. 


The  Principle  of  the  Safety  Lamp.  95 

Experiment— To  Illustrate  the  Action  of  Gauze, 

Take  a  block  of  wood  and  fix  into  it  a  number  of  small 
brass-headed  screws  or  tacks  closely 
packed  so  as  to  represent  gauze  (see 
Fig.  54).  Level  off  any  unevenness 
of  surface  by  a  file  or  stone.  Paste 
a  sheet  of  paper  on  the  block  and 
when  dry  hold  it  over  a  Bunsen  flame 


for   a    few    seconds    and    notice    any      FlQ  54>_Screws  and  in- 
charring  of  the  paper.  terspaces  to  represent 

gauze. 

The  charring  of  the  paper  will  depend  on  its  getting 
heated,  but  if  the  heat  be  quickly  and  regularly  led  away 
from  the  paper  by  the  metal  then  charring  cannot  occur. 
The  wood  does  not  lead  away  the  heat  and  so  the  paper 
over  it  quickly  chars.  Brass  is  therefore  a  better  material 
than  wood  for  leading  away  heat  (see  the  Table  on  p.  91). 

Let  us  try  and  follow  what  happens  as  the  heat  leaves 
the  flame  at  those  places  where  there  are  tacks.  The  heat 
passes  through  the  paper  and  is  quickly  led  away  along  the 
tack,  and  if  the  points  of  the  tacks  go  through  the  block, 
as  they  should,  then  the  heat  will  pass  into  the  air.  It  is 
of  great  importance  to  know  whether  the  air  remains  fixed 
and  the  heat  is  discharged  into  it,  or  if  it  moves  away  and 
carries  heat  with  it.  If  the  latter  is  true  then  the  heat  will 
not  accumulate  around  the  ends  of  the  tacks  for  the  air,  as 
convection  currents,  will  move  away  with  the  heat  taken  up 
by  it. 

Cooling  Hot  Bodies  by  Metallic  Surfaces, 

The  cylinders  of  small  engines  in  which  mixtures  of  gas, 
or  petrol  vapour,  and  air  are  fired  would  become  very  hot 
if  no  devices  for  cooling  were  used.  In  the  engines  of 
aeroplanes  and  motor  cycles  fins  or  ribs  are  cast  on  the 
cylinder  so  as  to  help  the  cooling  of  the  latter ;  the  bigger 
the  surface  exposed  the  sooner  the  engine  gets  rid  of  waste 
heat.  Travelling  through  the  air  is  a  great  aid  to  cooling. 

In  motor-cars  there  is  a  radiator  in  front  of  the  car  on 
which  are  fins  or  ribs  for  helping  the  cooling  of  the  water 
which  brings  heat  away  from  the  cylinder  of  the  engine. 


g6  An  Introduction  to  Mining  Science. 

This  water  can  be  used  over  and  over  again  for  taking  away 
heat  from  the  cylinder. 

The  foregoing  instances  should  help  us  to  realize  that 
having  a  big  surface  exposed  to  the  air  helps  a  hot  body  to 
cool  quickly.  Compare  these  devices  with  that  of  having 
if  oz.  of  iron,  less  than  half  of  a  cubic  inch,  made  into  2016 
inches  having  an  area  of  95  sq.  inches  for  cooling  the  hot 
gases  produced  in  a  miner's  lamp.  Spreading  out  a  hot 
body  to  the  air  greatly  assists  its  cooling — the  surface  of 
the  bonnet  is  an  illustration  of  such. 

By  experiment  and  experience  it  has  been  shown  that  a 
heated  body  may  lose  heat  in  two  ways — by  the  air  carry- 
ing  heat  away  as  it  moves  from  the  body,  and  by  a  fixed 
part  leading  heat  along  it  more  or  less  easily  according  to 
power  called  conductivity. 

Air  is  a  good  carrier  but  a  poor  conductor  (see  p.  91) ; 
it  can  move  because  it  is  a  gas.  A  solid  cannot  move,  it 
cannot  therefore  carry  away,  it  can  only  let  heat  flow  along. 

An  Illustration  of  Conduction  and  Convection, 

Imagine  a  large  reservoir  of  water  from  which  are  laid  pipes 
to  distribute  the  water  to  a  district.  Then  for  this  purpose  we 
may  say  that  the  pipes  lead  or  conduct  the  water  from  the  source  ; 
they  are  conductors  of  water.  The  reservoir  may  also  lose  water 
in  another  way — by  winds  blowing  across  its  surface,  carrying 
with  them  moisture.  From  this  point  of  view  the  moving  air  is 
the  vehicle  by  which  water  is  removed  ;  it  is  analogous  to  a 
convection  current  of  air  carrying  away  heat  from  a  hot  body. 

Both  conduction  and  convection  help  to  keep  a  miner's 
lamp  cool.  There  is  a  third  way  by  which  heat  may  be 
lost  by  a  body ;  this  way  is  the  only  one  by  which  the  sun's 
heat  is  lost  to  it  and  reaches  us. 

Air  does  not  fill  all  the  space  between  us  and  the  sun, 
so  there  can  be  no  convection  currents  to  bring  its  heat, 
and  there  is  no  solid  material  in  space  to  conduct  it  to  us. 
Heat  that  comes  across  a  space,  empty  or  containing  air, 
and  does  not  heat  it,  is  spoken  of  as  radiant  heat ;  the  pro- 
cess is  known  as  radiation. 

A  room  with  a  fire  is  not  alone  heated  by  convection 
currents  of  air,  but  by  heat  cutting  through  the  air  inde- 


The  Principle  of  the  Safety  Lamp. 


97 


pendently  of  the  latter's  existence,  i.e.  by  radiation.  A 
lamp  will  lose  heat  by  conduction  through  the  metal  by 
convection  in  the  air,  and  by  radiation  through  the  sur- 
rounding space. 

Convection  Currents. 

The  movement  of  air  and  its  power  of  carrying  away  with 
it  heat  is  taken  advantage  of  in  ventilating  public  rooms ; 
Fig.  55  shows  a  ring  of  gas  burners  under  a  large  funnel,  its 
flue  projecting  beyond  the  roof  into  the  outer  air. 


FIG.  55. — The  arrows  denote  the  general  direction  of  the  currents. 

The  heat  of  the  gas  is  therefore  carried  away  by  convec- 
tion currents  of  air  ;  their  directions  are  shown  by  arrows. 

A  liquid  like  air  can  move  when  heated  and  so  carry  heat 
by  its  currents.  These  currents  may  be  easily  seen  if  a 
substance  which  only  dissolves  slowly  is  put  in  the  liquid. 

Experiment, 

Fit  up  the  apparatus  shown  in  Fig.  56.  Fill  the  flask  with 
water,  drop  into  it  a  few  crystals  of  permanganate  of  potash,  and 
then  heat  with  a  small  flame. 


An  Introduction  to  Mining  Science. 


FIG.  56. — Showing  the  use  of  water 
as  a  carrier  of  heat. 


Heat  is  carried  about  by 
the  moving  water  currents  ; 
their  directions  are  shown 
by  streaks  of  coloured 
water. 

The  gauze  is  used  over 
the  burner  (as  in  Fig.  56) 
whenever  a  thin  glass  ves- 
sel is  being  used  for  heat- 
ing a  liquid,  as  it  prevents 
the  flame  playing  directly 
on  the  glass,  owing  to  the 
difficulty  it  has  in  getting 
through  the  gauze.  If  the 
gauze  gets  very  hot  and  the 
flame  gets  partly  through, 
the  flame  is  still  well  kept 
back  and  therefore  cannot 
usually  rise  higher  than  the 
surface  of  the  water,  so  the 
vessel  is  preserved  from 
this  danger  and  probably 
from  being  broken. 


Practical  Application  to  Mining. 
Safety  Lamps, 

The  problem  of  how  to  secure  a  safe  and  efficient  light 
for  the  miner  has  engaged  the  attention  of  mining  and 
scientific  men  for  nearly  two  hundred  years.  Owing  to  the 
use  of  naked  lights  in  mines  where  inflammable  gas  was 
present  in  dangerous  quantities  many  serious  explosions  oc- 
curred. In  1740  the  steel  mill,  a  device  for  lighting  gassy 
mines,  was  introduced  by  Spedding ;  this  consisted  of  a 
steel  wheel  driven  by  hand  by  means  of  gearing  which  on 
being  rotated  rubbed  against  a  flint  and  threw  off  a  shower 
of  sparks.  The  light  obtained  in  this  way  was  feeble  and 
in  some  cases  the  sparks  were  sufficiently  hot  to  ignite  an 
inflammable  mixture  of  air  and  gas. 


The  Principle  of  the  Safety  Lamp. 


99 


In  181 1  Clanny  invented  a  lamp  in  which  the  light  burned 
in  an  airtight  vessel,  the  air  necessary  for  combustion  being 
supplied  by  a  pair  of  bellows. 

In  1813  public  opinion  had  become  so  aroused  by  the 
frequent  occurrence  of  colliery 
explosions  that  a  society  was 
formed  in  the  North  of  Eng- 
land with  the  object  of  calling 
the  attention  of  scientific  men 
to  these  disasters  and  of  ob- 
taining their  help  in  minimiz- 
ing them.  The  result  of  the 
labours  of  this  society  was 
seen  in  the  invention  of  the 
Davy  and  Stephenson  lamps, 
and,  a  little  later,  the  Clanny 
lamp. 

The  Davy  lamp  consists  of  an  oil  vessel  surmounted  by 
a  cage  of  gauze,  the  necessary  air  for  combustion  passing  in 
and  out  of  the  lamp  through  the  gauze. 

The  Stephenson  lamp  is  similar,  but  in  addition  to  the 
gauze  is  fitted  with  an  internal  cylindrical  glass  with  a 


FIG. 


57. — Davy  lamp,  photo- 
graph and  diagram. 


FIG.  58. — Stephenson  lamp,  photo- 
graph and  diagram. 


FIG.     59.  —  Clanny     lamp, 
photograph  and  diagram. 


perforated  cap  of  copper.  The  air  for  combustion  enters 
the  lamp  through  a  series  of  small  holes  near  the  bottom 
and  passes  out  at  the  top  of  the  lamp. 

7* 


loo          An  Introduction  to  Mining  Science. 


In  the  Clanny  lamp  the  light  is  surrounded  by  a  thick 
glass  cylinder  surmounted  by  a  gauze,  and  the  air  passes 
into  the  lamp  just  above  the  glass  and  out  at  the  top. 

These  lamps  are  not  now  used  in  mines,  as  they  are 
unsafe  in  explosive  mixtures  of  air  and  gas  even  if  such 
are  travelling  at  comparatively  low  velocities,  and  they 
do  not  comply  with  the  requirements  of  the  Coal  Mines 
Act. 

In  1840  a  Belgian  mining  engineer  named  Meuseler  in- 
troduced an  improved  safety  lamp, 
the  improvement  consisting  of  a  gauze 
diaphragm  fitting  just  above  the  glass 
and  carrying  a  metal  chimney. 

Air  passes  into  the  lamp  through  the 
outer  gauze,  through  the  gauze  dia- 
phragm to  the  light,  and  out  by  way 
of  the  chimney.  This  lamp  was  found 
to  be  safer  than  those  previously  de- 
scribed. 

It  was  subsequently  modified  and 
remodelled  by  M.  Marsaut,  a  French 
mining  engineer,  the  principal  altera- 
tions being  the  removal  of  the  chimney 
and  gauze  diaphragm  and  the  substitu- 
tion of  an  inner  gauze. 

Most  of  the  safety  lamps  of  the  pre- 
sent day  are  of  the  Meuseler  or  Mar- 


saut   type,    and    they   are    nearly    all 


FIG.  60. — Photograph 
of  Meuseler  chim- 
ney lamp,  glass,  and 

shielded  or  bonneted  as  a  protection 
from  the  high  velocities  now  prevalent. 

A  modern  safety  lamp  (Fig.  61)  should  give  a  good  light, 
should  be  simple  in  construction,  and  not  easily  extinguished 
accidentally,  but  self-extinguishing  in  an  explosive  atmos- 
phere, and  should  be  so  protected  by  means  of  a  bonnet  and 
suitable  baffle  plates  at  the  air  inlets  as  to  be  safe  in  an 
explosive  mixture  travelling  at  any  velocity  likely  to  be  met 
with  in  a  mine  and  striking  the  lamp  at  any  angle. 

It  should  be  fitted  with  a  good  lock  which  cannot  easily 
be  tampered  with,  and  should  also  be  carefully  looked  after 


Wire  Gauze. 


The  Principle  of  the  Safety  Lamp.  101 

and  kept  clean,  as  its  safety  in't&e  presence  of  gas  depends 
upon  it  being  in  good  condition.1 

It  is  very  important  that  the 
direction  of  the  air  through  a 
safety  lamp  should  be  studied  so 
that  in  the  event  of  it  becoming 
necessary  to  extinguish  a  lamp 
owing  to  gas  firing  or  exploding 
in  it,  this  may  be  done  readily 
and  safely  by  covering  up  all  the 
air  inlet  holes  (see  Fig.  61)  with 
some  article  of  clothing. 

The  provisions  of  the  Coal  Mines 
Act  require  that  no  light  other  than 
a  locked  safety  lamp  shall  be  used 
in  a  seam  where  any  return  airway 
contains  more  than  -J  per  cent  of 
inflammable  gas,  or  in  any  seam 
(except  in  main  airways  within  200  yards  from  the  shaft) 
where  an  explosion  of  inflammable  gas  causing  personal  in- 
jury has  occurred  within  the  previous  twelve  months,  or  in 


Air  enters. 


FIG.  61.  —  Diagram  of 
lamp,  showing  air  cur- 
rents and  construction. 


FIG.   62. — Photograph  of  lamp   ring,   showing  air   inlets  and  baffle 
plate.     The  ring  is  cut  in  order  to  show  section. 

any  place  where  there  is  likely  to  be  any  such  quantity  of 
gas  as  to  render  the  use  of  naked  lights  dangerous. 

Lamps  must  not  be  unlocked  underground  except  at  the 
appointed  lamp  station,  which  must  not  be  in  the  return  air. 

1  For  particulars  and  drawings  of  modern  lamps  see  Safety  Lamps 
Order  issued  by  Home  Office,  Form  886. 


IO2  An  Introduction  tc  Mining  Science. 

A  person  using  a  safety  lamp  'must  examine  it  externally 
and  see  that  it  is  locked  and  in  good  order  before  entering 
the  mine,  and  must  from  time  to  time  examine  the  lamp  to 
see  that  it  is  in  safe  working  order.  If  the  lamp  is  injured 
while  in  his  possession  he  must  at  once  carefully  extinguish 
the  light. 

The  Electric  "  Miner's  Lamp  ". 

The  portable  electric  lamp  has  been  used  in  mines  to  a 
small  extent  for  a  considerable  number  of  years,  but  recently, 
owing  to  the  demand  for  a  better  light,  the  number  in  use 
has  greatly  increased,  and  appears  likely  to  increase  still  more 
in  the  future.  It  gives  a  very  good  light  but  cannot  at 
present  be  used  for  detecting  fire-damp. 

The  lamp  consists  essentially  of  the  following  parts : — 

1.  A  case,  usually  of  steel. 

2.  An  electrical  accumulator  or  cell. 

3.  A  bulb  of  glass  carrying  the  wire  or  filament  which 
gives    light   by   becoming   incandescent  when   an    electric 
current  is  passed  through  it. 

4.  A  suitable  and  efficient  locking  arrangement. 

The  accumulator  or  cell  consists  of  two  plates  of  metal 
which  dip  into  a  liquid.  If  a  current  of  electricity  is 
passed  into  one  plate  through  the  Jffjuid  and  out  at  the 
other  plate,  chemical  changes  take  place -and  the  energy 
expended  by  the  electric  current  is  stored  up  in  the  lamp 
and  may  be  given  out  as  required.  The  cell  of  an  electric 
miner's  lamp  must  be  charged  every  day  by  passing  through 
it  an  electric  current. 

The  two  principal  types  of  lamp  are  the  Alkaline  Lamp 
and  the  Lead  Accumulator  Lamp.  In  the  former  the 
liquid  used  in  the  cell  is  alkaline,  and  the  metal  used  in  the 
making  of  the  plates  may  be  nickel,  cobalt,  cadmium,  and 
iron.  In  the  latter  the  liquid  used  is  acid,  and  the  metal 
of  the  plates  is  lead. 

Both  types  of  lamp  are  illustrated  in  Figs.  63  and  64, 
which  are  photographs  of  lamps  now  widely  used. 

The  alkaline  lamp  is  said  to  have  a  candle-power  of 
175  and  the  lead  accumulator  lamp  a  candle-power  of  1-5. 


The  Principle  of  the  Safety  Lamp.  103 

It  will  be  noticed  that  in  both  lamps  the  bulb  carrying 
the  light  is  surrounded  by  a  stout  protecting  glass  which 
cannot  be  easily  broken. 


FIG.  63.— Wolf  alkaline  lamp. 


FIG.  64. — Wolf  lead  accumulator 
lamp. 


IO4  An  Introduction  to  Mining  Science. 

QUESTIONS. 

1.  What  are  the  disadvantages  of  having  too  high  a  flame  in  a 
safety  lamp  ? 

2.  Describe  the  kind  of  safety  lamp  the  men  use  in  the  mine  where 
you  work.    Does  it  differ  from  that  used  by  the  foremen  ;  if  so,  in  what 
manner  ? 

3.  What  might  be   the  effect  of  accidentally  leaving  the  gauzes 
out  of  a  lamp  when  in  use  ? 

4.  In  putting  together  a  lamp  the  glass  might  be  fixed  tightly  with- 
out its  being  gas-tight.     How  would  you  test  to  see  if  the  glass  is 
fixed  gas-tight  ? 

5.  How  may  lamp  gauzes  be  injured  and  rendered  dangerous  to  use 
in  the  pit  ? 

6.  What  effects  has  too  high  a  flame  on  the  crown  of  the  gauze  ? 
How  would  you  test  to  see  if  the  gauze  has  been  damaged  in  this 
manner  ? 

7.  What  substances  are  likely  by  use  to  be  deposited  on  the  gauze 
of  a  miner's  lamp  ?     Do  they  affect  the  safety  of  the  lamp  ? 

8.  Is  the  mine  you  work  in  a  gassy  or  a  non-gassy  one  ?     Do 
you  think  the  same  carefulness  should  be  exercised  by  miners  and 
managers  in  both  kinds  of  mine  ? 

9.  Soot,  coal  dust,  and  charred  oil  are  often  found  on  a  lamp  gauze. 
Do  you  think  there  is  danger  in  allowing  them  to  remain  on  the  gauze  ? 
What  is  the  danger  to  be  feared  ? 

10.  Gauzes  are   made  of  copper  and  iron,  as  are  kettles.     Give 
reasons  for  the  use  of  these  two  metals  in  either  article. 

11.  Where  does  all  the  heat  ot  the  lamp  get  to  finally  ?     How  does 
the  heat  get  away  ?     Would  the  lamp  keep  as  cool  if  the  air  did  not 
move  when  heated  ? 

12.  Does  the  handle  of  your  lamp  become  warm  ?     Account  for  the 
result  of  your  observation. 

13.  Which  kind  of  tub  is  the  colder  to  the  touch — an  iron  or  a 
wooden  one  ?     Explain  why  there  is  a  difference. 

14.  What  objection  is  there  to  a  metal  teacup  ?     Do  you  consider 
copper  to  be  the  best  metal  for  use  in  making  cylinders  to  hold  hot 
water  ? 

15.  In  what  way  may  a  defective  gauze  differ  from  a  satisfactory 
one  ?     What  might  be  the  effect  of  using  a  defective  gauze  in  a 
lamp  ? 

16.  The  best  height  for   the  flame  of  a  safety  lamp  is  said  to  be 
about  f  of  an  inch.     What  reasons  are  there  for  fixing  this  as  the  best 
height  ? 

17.  What  gases  would   be   found   inside   a   miner's   lamp   before 
and  after  the  lamp  is  lighted  ? 

18.  Describe  how  to  examine  a  safety  lamp  to  see  if  it  is  in  working 
order.     What  parts  are  most  likely  to  get  out  of  order  ? 

19.  Explain  by  diagram  how  your  safety  lamp  gets  the  necessary 
supply  of  air.     Do  all  safety  lamps  get  air  by  the  same  method  ? 


CHAPTER  VI. 

THE  MINE  GASES  KNOWN  AS  DAMPS. 

THE  word  damp  can  be  traced  in  the  Dutch,  Danish,  and 
Low  German  languages ;  it  is  the  same  word  as  the  German 
dampf,  meaning  steam,  vapour,  fog  or  smoke.  At  the 
present  time  in  general  life  it  often  means  moisture,  but  in 
mining  it  suggests  dangerous  gases.  All  the  damps  are 
not  combustible  gases,  e.g.  black  or  choke-damp  will  not 
burn,  they  are  all  dangerous  to  life. 

Choke-damp, 

This  is  the  miner's  name  for  the  gas  carbon  dioxide  which 
has  been  considered  on  pp.  29-36. 

It  has  been  shown  in  these  pages  that  it  is  a  gas  much 
heavier  than  air,  hence  it  will  accumulate  near  the  floor 
and  at  the  bottom  of  sumps  or  wells.  It  is  known  to 
escape  sometimes,  like  fire-damp  does,  from  the  coal-face  in 
very  large  quantities. 

It  must  be  remembered  that  the  accumulation  of  this  gas 
on  the  floor  will  be  affected  by  the  ventilating  current  of  the 
mine,  and  also  by  its  own  power  of  diffusing.  If  we  imagine 
a  big  outburst  of  carbon  dioxide  from  the  coal- face  the  gas 
will  fall  towards  the  floor,  but  it  will  not  stay  there  per- 
manently ;  as  soon  as  the  outburst  is  over  diffusion  would 
slowly  clear  it  all  away,  the  ventilation  current  would  do 
it  quickly.  No  gas  will  stop  permanently  in  any  place, 
unless  in  an  airtight  enclosure ;  diffusion  always  spreads  it 
far  and  wide. 

Choke-damp  begins  to  be  objectionable  when  there  is  3 
to  4  per  cent  in  the  air;  at  6  per  cent  headache  is  felt. 
The  senses  become  more  or  less  drugged  as  the  quantity 

105 


106  An  Introduction  to  Mining  Science. 

increases,  and  15  per  cent  renders  one  unconscious.     Death 
will  occur  at  25  per  cent. 

Its  action  in  extinguishing  a  light  is  a  very  valuable  and 
simple  indication  of  its  existence  in  a  place. 

Marsh  Gas  or  Fire-damp, 

Marshes  are  low-lying  pieces  of  land  usually  of  a  swampy 
nature ;  the  soil  of  such  land  generally  contains  decompos- 
ing refuse  of  a  vegetable  nature,  and  all  vegetable  material 
when  sufficiently  decomposed  gives  off  gases,  one  of  which 
is  called  marsh  gas.  This  origin  of  the  gas  has  given  it  the 
first  name.  Decomposing  vegetable  material  accumulates  on 
the  bottom  of  ponds,  and  if  they  are  not  regularly  cleaned 
it  rots  further  and  produces  marsh  gas.  If  stagnant  and 
dirty  pools  are  watched  during  a  hot  summer  bubbles  will  be 
seen  rising  to  the  surface ;  these  are  bubbles  of  marsh  gas. 

Now  coal  is  vegetable  material  which  has  undergone 
through  long  ages  a  certain  amount  of  decomposition,  pro- 
ducing marsh  gas,  which  gets  liberated  and  mixes  with  mine 
air  when  the  coal  seams  are  worked. 

As  this  gas  takes  fire  when  mixed  with  air  it  is  sometimes 
called  "Fire,"  which  gives  the  reason  for  the  first  part  of  the 
word  fire-damp. 

In  olden  times,  even  at  the  end  of  the  eighteenth 
century,  it  was  got  rid  of  in  mines  by  setting  it  on  fire. 
The  men  set  off  for  this  special  kind  of  work  were  called 
firemen. 

Experience, 

That  the  air  in  its  ordinary  state  is  neither  combustible  nor 
explosive  follows  from  the  everyday  action  of  striking  a  match 
in  it,  or  producing  any  kind  of  a  light.  If  it  were  so,  then  it 
would  take  fire  where  the  light  is  and  spread  throughout  the 
atmosphere. 

It  is  plain,  then,  that  mine  air  differs  from  ordinary  air, 
inasmuch  as  a  light  may  produce  an  explosion,  which  is 
very  rapid  combustion,  the  whole  of  the  mine  air  being 
quickly  ablaze.  The  mine  air  in  these  circumstances  is 
similar  to  ordinary  air  mixed  with  coal  gas,  it  having  become 
combustible  and  explosive. 


The  Mine  Gases  known  as  Damps.  107 

Fire-damp  consists  wholly  or  chiefly  of  the  combustible 
gas  called  marsh  gas  or  methane ;  the  other  gases  mixed 
with  it  vary  in  amount  but  are  generally  small.  The  fol- 
lowing figures  show  the  composition  of  two  samples  of  fire- 
damp :— 

South  Wales  Colliery.    Gateshead  Colliery. 
Marsh  gas      .         .         97*7  per  cent  94-2  per  cent 

Nitrogen         .  i'8       „  nil 

Carbon  dioxide       .  '5      »  nu< 

Air        .         .         .          none  5-8 

lOO'O  lOO'O 

We  have  learnt  that  air,  carbon  dioxide,  and  nitrogen  are 
not  combustible,  and  it  is  plain  therefore  that  the  essential 
constituent  of  fire-damp  is  marsh  gas. 

The  following  figures  give  the  action  of  a  light  on  various 
mixtures  of  air  and  marsh  gas.  It  should  be  particularly 
noticed  that  mixtures  rich  and  poor  in  marsh  gas  are  not 
explosive.  The  first  mixture  is  equal  to  28'6  per  cent  of 
marsh  gas  and  is  rich  in  the  gas ;  the  last  one  only  contains 
2  per  cent,  and  is  therefore  poor ;  in  neither  case  is  there 
any  explosive  action  when  a  light  is  brought  into  contact 
with  the  mixture. 

Marsh  Gas.  Air.  Action  of  a  Light  on  the  Mixture, 

i  cub.  ft.  3-J  cub.  ft.  No  explosion  ;  burns  quietly. 

„  5£        „  Explodes  gently. 

„  9-J  „  Most  explosive. 

„  13  „  Explodes  gently. 

„  30  „  No  explosion. 

,,  50  „  No  explosion. 

The  last  two  correspond  to  2  and  3  J  per  cent  respectively, 
and  they  can  be  readily  detected  as  a  "  gas  cap "  by  the 
lowered  flame  of  a  miner's  lamp.  Thus  both  mixtures  burn 
in  proximity  to  a  source  of  light  and  heat — as  the  lamp  flame 
— but  they  will  not  explode,  neither  will  they  continue  burn- 
ing when  the  flame  is  withdrawn. 

If  the  actions  of  a  substance  have  to  be  learnt  it  is  neces- 
sary to  get  this  substance  free  from  others,  then  we  are 
quite  certain  that  there  will  be  no  erroneous  conclusions 


IO8  An  Introduction  to  Mining  Science. 


due  to  other  substances  being  present.  Fire-damp  always 
contains  marsh  gas  and  generally  other  gases,  and  so  if  a 
substance  which  easily  gives  off  marsh  gas  unmixed  with 
other  gases  can  be  found,  we  may  use  it  for  finding  some 
properties  of  the  dangerous  constituent  of  fire-damp. 

To  Make  Marsh  Gas. 

Fit  up  a  small  flask  with  a  thistle-head  tube  and  a  delivery  /-« 

tube  passing  through  the  cork. 
The  thistle-head  tube  should 
reach  almost  to  the  bottom  of  the 
flask,  and  the  delivery  tube  just 
through  the  cork  (see  Fig.  66). 
Place  about  1 5  gm.  of  aluminium 
carbide  in  the  flask  and  arrange 
to  collect  the  gas.  Pour  small 
quantities  of  water  through  the 
thistle  funnel — it  may  be  neces- 
sary to  slightly  warm  to  start  the 
action — and  collect  three  jars  of 
the  gas ;  keep  them  inverted. 
Apply  a  light  separately  to  the 
first  and  second  jars.  The  gas 
in  the  first  jar  may  give  a  slight 
explosion  owing  to  its  being 
mixed  with  air  obtained  from 
that  in  the  flask.  The  second 
jar  should  be  turned  upright  as 
soon  as  the  gas  has  been  lighted. 
Watch  the  flames  pass  down  the 
cylinder,  then  allow  to  cool,  with 
a  cover  glass  on,  and  shake  up 
with  lime  water  so  as  to  detect 
the  carbon  dioxide  produced 
FIG.  65.— Applying  a  light  to  a  in  the  combustion.  Push  the 
cylinder  of  marsh  gas.  Hghted  taper  jnto  the  ^^  -^ 

(see  Fig.  65).  In  the  case  of  the  third  jar  it  will  be  noticed 
that  there  is  no  explosion  ;  if  no  air  is  present  the  lighted  taper 
will  be  extinguished. 

The  foregoing  experiments  and  the  method  of  performing 
them  show  that  marsh  gas  is  lighter  than  air,  not  easily  dis- 
solved by  water,  is  combustible,  forms  an  explosive  mixture 


The  Mine  Gases  known  as  Damps. 


109 


with  air,  and  on  the  combustion   of  it  carbon  dioxide  is 
produced. 

In  the  combustion  water  vapour  is  also  formed,  but  as 
water  is  used  in  making  the  marsh  gas  the  experiment  cannot 


O 


FIG.  66. — Apparatus  for  preparing  marsh  gas. 

be  used  to  prove  its  formation  in  the  burning.  Some  water 
vapour  will  come  over  with  the  marsh  gas,  and  so  collecting 
it  in  a  dry  cylinder,  by  displacing  air,  would  not  prove  the 
point. 

Aluminium  Carbide. 

The  name  suggests  it  is  made  of  two  substances,  alu- 
minium and  carbon,  and  such  is  the  case.  Aluminium  may 
be  well  known  to  us  if  we  use  our  observational  powers,  for 
it  is  widely  used  in  making  saucepans,  kettles,  and  other 
domestic  metal-ware,  and  for  making  parts  of  petrol  engines. 

It  is  a  light  metal,  silvery-white  in  appearance,  and  may 
be  strongly  heated  without  undergoing  alteration  ;  it  is  neither 
affected  by  hot  nor  cold  water.  The  foregoing  properties 
should  be  noted  in  connection  with  a  saucepan  and  its 
work. 

Carbon  is  as  well  and  as  widely  known  as  aluminium ;  it  is 


no  An  Introduction  to  Mining  Science. 

our  old  friend  soot,  which  we  know  comes  from  coal. 
The  two  substances  aluminium  and  carbon  when  heated 
in  the  electric  furnace  at  about  3000°  C.  join  together  to 
form  a  new  substance  composed  of  them  and  therefore 
called  aluminium  carbide. 

Aluminium  is  the  most  abundant  of  all  the  metals ;  one 
source  of  the  metal  is  clay,  but  it  is  not  easily  got  out  of  this 
source.  Carbon  is  also  very  abundant ;  it  is  found  in  all 
animal  and  vegetable  substances. 

Calcium  carbide  is  a  substance  much  like  aluminium 
carbide ;  one  difference  is  the  presence  of  a  metal  called 
calcium  instead  of  aluminium.  Water  acts  on  both  carbides, 
and  liberates  gases — acetylene  in  the  case  of  calcium  carbide. 
There  are  scientific  men  who  believe  that  steam  acting  on 
carbides  deep  down  in  the  earth  may  produce  the  gases  found 
in  petroleum  wells,  and  even  petroleum  itself. 

Origin  of  Marsh  Gas  in  Mines,  etc, 

Most  coal  seams  contain  marsh  gas  (in  some  there  are 
very  large  amounts)  along  with  the  other  gases  which  com- 
pose fire-damp.  There  is  no  doubt  marsh  gas  in  mines  has 
had  its  origin  in  the  decay  of  coal ;  coal  seams  have  been  very 
largely  made  from  leaves  and  twigs  of  trees,  which  by  decay 
produce  marsh  gas. 

There  is,  as  has  just  been  pointed  out,  a  close  connexion 
between  the  decay  of  vegetable  matter,  with  no  air  present, 
and  the  production  of  marsh  gas.  In  the  decomposition  of 
wood  by  heating  it  in  the  absence  of  air  much  marsh  gas  is 
produced,  and  also  a  substance  called  acetic  acid.  Acetic 
acid  is  an  acid  derived  from  the  vegetable  world,  and  is 
closely  related  to  another  vegetable  acid — formic — which 
easily  gives  off  the  most  dangerous  of  all  damps — carbon 
monoxide.  In  the  similar  decomposition  of  coal  to  get  coal 
gas  there  is  much  marsh  gas  produced. 

Marsh  gas  may  be  made  in  the  chemical  laboratory  from 
acetic  acid ;  the  acid  is  first  mixed  with  soda  and  so  forms 
acetate  of  soda.  When  this  substance  is  heated  in  a  tube 
and  caustic  soda  is  present,  marsh  gas  comes  off  and  may 
be  collected. 


The  Mine  Gases  known  as  Damps.  ill 

Carbon    Monoxide  Gas. 

White  damp  is  the  miner's  name  for  this  gas ;  it  has  the 
scientific  name  carbon  monoxide.  This  name,  like  others 
in  chemistry,  tells  us  the  composition  of  the  gas  ;  it  contains 
only  carbon  and  oxygen.  Carbon  dioxide,  which  we  have 
studied,  is  made  of  carbon  and  oxygen,  but  there  is  twice 
as  much  oxygen  by  weight  in  it  as  in  carbon  monoxide. 
Compare  the  prefixes  of  the  words  monoplane  and  biplane 
to  denote  aeroplanes  having  one  and  two  planes  respec- 
tively. 

The  close  relationship  of  the  two  gases  in  name  should 
be  kept  in  mind ;  as  we  shall  see  one  may  turn  into  the 
other  by  changing  its  amount  of  oxygen.  Although  carbon 
dioxide  is  more  common  than  carbon  monoxide  it  is  very 
likely  that  we  are  more  familiar  with  the  latter,  owing  to  the 
striking  blueness  of  its  flame. 

Experience. 

Watch  the  flame  at  the  top  of  the  street-watchman's  fire ;  it 
has  a  blue  colour  similar  to  the  lower  blue  part  of  a  luminous  gas 
flame.  The  same  flame  may  be  seen  burning  when  the  fire  is 
red-hot  in  a  house  grate.  The  blacksmith's  forge  will  show  the 
same  blue  flame  when  the  coke  on  the  hearth  is  red-hot,  and  air 
is  being  forced  through  the  glowing  mass.  The  same  blue  flame 
may  often  be  seen  burning  at  the  outlet  of  a  smelting  furnace  flue. 
This  blue  flame  is  in  each  case  the  invisible  gas,  carbon  monoxide, 
burning. 

When  coal  or  coke  burns  with  a  plentiful  supply  of  air 
carbon  dioxide  is  produced,  and  it  might  be  said  in  the 
cases  given,  when  we  see  the  blue  flame  of  carbon  mon- 
oxide, there  is  a  plentiful  supply.  The  contention  is  quite 
true,  and  so  the  explanation  of  the  discrepancy  must  be 
sought  for  by  making  an  experiment,  and  in  so  doing  we 
shall  find  one  way  of  accounting  for  the  production  of  carbon 
monoxide  in  the  pit. 

Experiment. 

If  a  piece  of  glass  tubing  is  filled  with  coke  or  charcoal  and 
fixed  on  a  retort  stand,  as  is  shown  in  the  right  side  of  Fig.  67, 
and  is  slowly  heated  by  a  Bunsen  burner,  whilst  air  or  oxygen 
is  passing  through  carbon  dioxide  gas  is  formed. 


112          An  Introduction  to  Mining  Science. 

The  air  or  oxygen  in  passing  over  red-hot  charcoal  in 
unlimited  quantities  brings  about  combustion  of  the  charcoal 
with  the  production  of  carbon  dioxide. 

If  the  glass  tube  instead  of  being  joined  to  the  iron  tube 


FIG.  67. 

of  the  furnace  opened  on  the  left  hand  into  the  air  and  a 
match  were  held  at  the  opening,  the  gas  coming  through 
would  not  ignite  ;  it  would  put  out  the  light.  If  the  glass 
tube  dipped  into  a  glass  of  lime  water,  the  latter  would 
become  white,  again  showing  the  gas  to  be  carbon  dioxide. 

The  Experiment  Continued, 

Fig.  67  shows  on  its  left  side  a  gas  furnace  through  which  runs 
a  piece  of  iron  pipe  also  filled  with  coke  or  charcoal.  The  figure 
shows  the  glass  tubing  fitted  into  the  iron  tube.  The  coke  in  the 
iron  tube  is  made  red-hot  by  the  gas  furnace,  and  then  carbon 
dioxide,  made  in  the  glass  tube,  passes  through  the  iron  tube.  It 
is  found  that  the  gas  issuing  from  the  iron  pipe  may  be  lighted, 
as  shown  in  the  figure. 

The  gas  coming  through  burns  with  a  blue  flame  and  is 
carbon  monoxide.  This  experiment  will  explain,  if  thoroughly 
understood,  the  formation  of  carbon  monoxide  in  the  house 
fire-grate,  in  the  watchman's  fire,' and  in  the  smith's  forge. 
When  carbon  monoxide  is  burning  at  the  exit  (Fig.  67)  the 
charcoal  or  coke  in  both  tubes  is  red-hot  and  air  or  oxygen 
is  passing  through  forming  carbon  dioxide  in  the  glass  tube, 
which  goes  into  the  iron  tube  full  of  red-hot  coke ;  this  takes 


The  Mine  Gases  known  as  Damps.  1 1 3 

away  from  the  carbon  dioxide  half  of  its  weight  of  oxygen  and 
so  transforms  it  into  carbon  monoxide.  When  this  carbon 
monoxide  gets  into  the  air  and  burns  it  becomes  carbon 
dioxide  again. 

Making  a  Diagram  to  give  an  Explanation, 

Represent  by  a  diagram  from  the  following  statement  a  section 
of  a  fire-grate.  Draw  three  small  circles,  representing  the  bars 
A,  B,  C,  about  the  size  of  the  head  of  a  nail,  and  half  an  inch 
above  each  other.  Draw  a  straight  line  about  half  an  inch  long 
from  the  lowest  circle  C,  leaving  a  few  gaps  in  it  to  represent  the 
spaces  of  the  under-grate  ;  from  the  end  draw  upwards  a  line, 
leaning  away  from  the  circles,  to  represent  the  back  of  the  fire- 
place. Fill  the  grate  with  the  outline  of  pieces  of  coal. 

With  the  foregoing  diagram  follow  through  this  explanation. 
The  air  passes  into  the  fire  by  the  under-grate  and  between 
the  bars  B  and  C  ;  put  arrows  in  the  diagram  to  represent 
these  two  air  streams.  In  these  lower  parts  of  the  fire  the 
air  and  coal  burn  forming  carbon  dioxide.  The  carbon 
dioxide  passes  forward  into  the  hot  mass  of  burning  coal 
about  on  a  level  with  the  bar  B,  and  gets  changed  to  carbon 
monoxide.  When  this  carbon  monoxide  appears  at  the  sur- 
face it  burns  with  a  blue  flame  to  carbon  dioxide.  The  pas- 
sage of  air  through  the  fire  is  therefore  precisely  similar  to  its 
passage  through  the  tubes  of  the  furnace ;  first  carbon  dioxide 
is  made  and  then  changed  to  carbon  monoxide,  and  then  again 
carbon  dioxide  is  produced.  So  carbon  monoxide  has  only 
a  short  existence. 

It  is  important  to  notice  that  in  each  case  the  flame  is  pro- 
duced from  either  burning  coke  or  coal;  the  former  is  made 
from  the  latter,  so  is  much  the  same  thing.  The  same  blue 
flame  may  be  produced  by  burning  paper  or  wood  ;  it  is  par- 
ticularly noticeable  when  the  material  gets  completely  hot. 
The  foregoing  substances  are  all  derived  from  the  vegetable 
world ;  there  are  some  chemicals  derived  from  the  vegetable 
world  which  by  other  treatment  than  burning  yield  carbon 
monoxide  gas. 

It  is  necessary  that  we  should  know  a  few  properties  of 
carbon  monoxide,  and  for  convenience  other  substances  than 
coal  or  coke  will  be  used  for  obtaining  the  gas,  but  like  coal 

8 


114  An  Introduction  to  Mining  Science. 

they  come  from  the  vegetable  world.  There  are  two  acids, 
formic  acid  and  oxalic  acid,  from  which  carbon  monoxide 
can  be  easily  got ;  the  former  is  the  acid  found  in  stinging 
nettles  and  the  latter  one  is  found  in  rhubarb.  The  acids 
may  be  used,  or  compounds  of  them  containing  soda,  called 
respectively  oxalate  of  soda  and  formate  of  soda.  Any  one 
of  the  four  substances — oxalic  acid  is  the  cheapest  because  it 
can  be  made  from  sawdust — when  mixed  with  strong  sulphuric 
acid  decompose  and  give  off  carbon  monoxide. 

To  Set  Free  Carbon  Monoxide, 

Fit  up  a  test  tube  A,  or  a  small  flask  B,  with  a  cork  and  delivery 
tube  (see  Fig.  68).  Place  in  the  test  tube  about  a  salt-spoonful  of 
soda  formate  and  about  the  same  bulk  of  strong  sulphuric  acid. 
Place  the  delivery  tube  in  water,  fill  a  test  tube  with  water,  then 
warm  the  mixture  and  collect  a  test  tube  full  of  the  gas.  Light  it  and 


FIG.  68. — Apparatus  for  setting  free  carbon  monoxide. 

notice  the  colour  of  the  flame,  and  test  the  burnt  gas  for  carbon 
dioxide  by  shaking  the  tube  after  adding  lime  water. 

Show  by  collecting  another  tube  full  that  the  original  gas  does 
not  give  with  lime  water  a  white  turbidity. 

The  gas  may  be  liberated  in  the  same  way  from  oxalic  acid ; 
in  this  case  carbon  dioxide  is  also  liberated  ;  prove  this  by  the 
lime-water  test  before  burning  the  carbon  monoxide. 

In  this  case  the  carbon  monoxide  may  be  burnt  as  it  leaves 
the  mouth  of  the  tube  containing  the  mixed  substances. 


The  Mine  Gases  known  as  Damps.  115 

Properties  of  Carbon  Monoxide. 

Carbon  monoxide  is  a  colourless  gas  which  burns  with  a 
blue  flame.  It  is  a  very  poisonous  gas,  giving  the  blood  a 
bright  scarlet  colour.  It  has  no  effect  in  small  quantities 
on  a  miner's  lamp. 

Formation  of  Carbon  Monoxide  in  the  Mine, 

Mine  air  invariably  contains  methane  and  coal  dust,  and 
in  the  course  of  an  explosion  they  take  up  oxygen ;  if  there 
is  insufficient  oxygen  to  form  carbon  dioxide,  then  carbon 
monoxide  is  produced.  If  methane  could  always  explode 
with  about  ten  times  its  bulk  of  air — exactly  the  proportions 
are  9*38  per  cent  of  methane  and  90 '62  per  cent  of  air — 
then  carbon  dioxide  would  be  produced.  In  explosive 
conditions  these  proportions  are  not  usually  found,  there  is 
a  shortage  of  oxygen  and  consequently  carbon  monoxide  is 
formed.  And  even  if  some  carbon  dioxide  were  originally 
formed  in  an  explosion  it  might  get  reduced  to  carbon 
monoxide  ;  this  is  proved  possible  by  the  Furnace  experiment 
and  the  changes  carbon  dioxide  undergoes  in  a  grate  full 
of  red-hot  coal  or  coke. 

Effect  of  Carbon  Monoxide  on  Man, 

Its  effects  on  men  are:  headache  at  first,  followed  by 
inability  to  talk,  and  finally  unconsciousness.  Any  quantity 
greater  than  "15  per  cent  is  distinctly  dangerous,  i.e.  about 
one  cubic  inch  in  700  cubic  inches  of  air,  -03  per  cent,  i.e. 
one  cubic  inch  in  3500  cubic  inches  of  air,  will  cause  giddiness. 

Dr.  Haldane  believes  that  on  an  average  70  out  of  every 
100  lives  lost  in  mine  explosions  are  due  to  poisoning  by 
carbon  monoxide ;  it  is  plain  then  that  it  is  formed  in  ex- 
plosions and  by  breathing  it  the  human  being  is  poisoned. 
In  the  West  Stanley  explosion  of  1909  when  165  men  were 
killed,  the  numbers  were  as  follows  : — 

Killed  by  carbon  monoxide  poisoning    121 

,,       ,,    violence     .         .       <  .  25 

Other  causes  of  death        .         .         .     19 


Ii6  An  Introduction  to  Mining  Science. 

Blood  in  the  lungs  absorbs  oxygen  from  the  air  in  them ; 
this  is  necessary  for  life,  but  in  the  presence  of  carbon 
monoxide  it  shows  preference  for  the  latter  gas,  despite  its 
poisonous  properties.  Blood  holds  carbon  monoxide  two 
hundred  times  more  firmly  than  it  does  oxygen. 

An  Analogy, 

That  different  substances  may  be  absorbed  and  then  held 
with  varying  degrees  of  firmness  may  be  illustrated  in  the 
following  manner.  A  spot  of  ink — and  ink  consists  of  water  con- 
taining a  soluble  black-blue  dye — falls  upon  a  piece  of  material, 
e.g.  cloth,  and  is  absorbed  by  the  material ;  in  time  the  water 
evaporates  away,  but  the  "  ink  stain  "  remains  ;  it  is  often  difficult 
to  remove  it  from  the  cloth.  Thus  the  water  is  less  firmly  held 
than  the  stain,  and  the  cloth,  therefore,  shows  a  holding  preference 
for  the  dye. 

Blood  in  the  same  way  holds  carbon  monoxide  more  firmly 
than  oxygen,  and  shows  its  preference  for  carbon  monoxide  by 
discarding  oxygen. 

A  Study  of  Stink-damp, 

Experiment. 

The  apparatus  and  method  used  for  carbon  monoxide  will 
be  satisfactory.  Place  in  the  tube  a  small  quantity  of  iron  sul- 
phide and  cover  with  dilute  sulphuric  acid.  Show  that  the  gas 
is  combustible,  and  notice  the  products  of  the  burning. 

Dip  a  piece  of  blotting-paper  into  lead  acetate  solution,  made 
by  dissolving  lead  acetate  in  water,  and  notice  the  blackening 
produced  by  the  gas  when  the  paper  is  held  above  the  mouth  of 
the  tube. 

This  gas  has  a  most  offensive  smell  resembling  the  odour 
of  rotten  eggs,  and  therefore  may  easily  be  detected  by  the 
nose.  The  other  simple  way  of  detecting  it — by  the  black 
colour  it  produces  on  a  paper  soaked  in  lead  acetate  solution, 
or  on  any  silver  which  you  happen  to  have — is  worth  noticing. 
Compare  these  two  easy  ways  of  recognizing  stink-damp  with 
the  difficulty  of  detecting  fire-damp,  which  has  no  smell  and 
no  effect  on  paper  dipped  into  any  solution.  Stink-damp 
often  occurs  in  fire-damp  in  small  quantities ;  if  it  were 
always  present  its  detection  would  be  a  clue  to  the  presence 
of  fire-damp. 


The  Mine  Gases  known  as  Damps.  117 

The  smell  of  stink-damp  is  often  noticed  when  rock  or 
coal  is  struck  by  a  hammer.  This  is  undoubtedly  due  to  there 
being  small  quantities  of  iron  sulphide  in  the  material 
struck.  The  occurrence  of  sulphuretted  hydrogen  in  mine 
air  or  iron  sulphide  in  coal,  is  not  very  difficult  to  explain. 
Vegetable  substances  contain  sulphur,  hydrogen,  and  iron ; 
in  their  decomposition  small  quantities  of  sulphuretted 
hydrogen  and  iron  sulphide  may  be  formed.  The  same  may 
be  said  of  some  animal  substances,  e.g.  eggs. 

Experience. 

You  have  probably  noticed  a  silver  spoon  will  blacken  when 
used  in  eating  an  egg,  and  that  an  oil  painting  darkens  with  age. 
In  each  case  it  is  stink-damp  ;  in  the  egg  coming  from  the  yolk,  and 
in  the  case  of  the  picture  coming  from  the  house  gas. 

The  well-known  smell  of  decomposing  cabbage,  or  greens 
of  any  kind,  is  often  due  to  the  presence  of  sulphuretted 
hydrogen. 

Stink-damp  is  also  found  in  the  gas  evolved  from  gob 
fires  and  in  the  blasting  of  powders. 

It  is  a  gas  that  very  easily  ignites  ;  a  temperature  half 
of  that  necessary  for  igniting  hydrogen  gas,  marsh  gas,  and 
carbon  monoxide  is  sufficient.  Small  quantities  of  this  gas 
will  quickly  produce  giddiness  and  vomiting,  and  finally 
death.  It  is  five  times  more  poisonous  than  carbon  mon- 
oxide. 

Iron  sulphide  often  reveals  its  presence  in  coal  by  ex- 
ploding in  the  fire-grate  and  being  shot  into  various  parts 
of  the  room.  In  the  absence  of  air,  iron  sulphide  may  be 
formed  by  sulphur  and  iron  attacking  each  other.  We  have 
seen  by  the  experiment  that  from  iron  sulphide  sulphuretted 
hydrogen  can  be  obtained. 

The  foregoing  helps  to  show  how  this  gas  may  arise  in 
the  decomposition  of  that  very  much  altered  vegetable  ma- 
terial called  coal. 

The  Gas  Called  Hydrogen. 

Hydrogen  is  a  gas  which  only  occurs  in  mine  air  in  very 
small  quantities ;  it  is  produced  in  blasting  operations  and 
is  also  found  in  fire-damp  in  small  quantities.  Hence  it  is 
studied  in  this  chapter  although  it  is  not  spoken  of  as  a  damp. 


Ii8  An  Introduction  to  Mining  Science. 

Explosive  Force  of  Hydrogen, 

Fit  up  a  soda-water  bottle  with  a  loosely  fitting  cork  and  a 
short  glass  tube  passing  through  the 
latter  (see  Fig.  69).  Place  into  the 
bottle  a  small  amount  of  dilute  sulphuric 
acid  and  zinc.  Allow  the  action  to  pro- 
ceed for  half  a  minute,  then  wrap  up  the 
bottle  in  a  duster  and  apply  a  light  to 

in  the 


uster*  It  is  a  colourless  gas,  violently 

explosive  ;  when  being  liberated  from  sulphuric  acid  by  the 
metal  zinc  the  bubbles  are  easily  seen  rising  up  through 
the  liquid. 

Hydrogen  occurs  in  coal  gas  to  the  extent  of  about  50  per 
cent,  and  as  there  is  a  large  quantity  of  marsh  gas  in  it 
one  may  expect  coal  gas  to  be  very  explosive. 

Hydrogen  is  not  of  much  importance  to  the  miner,  but 
a  knowledge  of  it  is  necessary  on  account  of  its  being 
a  constituent  of  marsh  gas  and  sulphuretted  hydrogen. 
The  latter  is  hydrogen  which  having  taken  up,  or  fixed, 
some  sulphur  is  therefore  called  sulphuretted  hydrogen. 
Sulphurized  rubber  is  similarly  made  from  rubber  and 
sulphur.  Marsh  gas  is  sometimes  called  carburetted  hydrogen 
because  its  constituents  are  carbon  and  hydrogen. 

Hydrogen  is  the  lightest  of  all  substances,  and  so  if  its 
heaviness  is  represented  by  one,  it  follows  the  heaviness 
of  all  other  gases  must  be  represented  by  a  bigger  figure. 
We  may  therefore  write  down  a  few  important  gases  as 
an  illustration  :  — 

Hydrogen  .  .        i  Marsh  gas      ...       8 

Nitrogen  .  .     -14  Carbon  monoxide  .          .14 

Oxygen  .  .16  Carbon  dioxide       .          .22 

Air      .  .  .14*4  Sulphuretted  hydrogen   .      17 

The  table  tells  us  how  much  heavier  than  hydrogen  is 
an  equal  bulk  of  any  of  the  gases  mentioned, 


The  Mine  Gases  known  as  Damps.  119 

After-damp, 

This  word  refers  to  the  gases  of  the  mine  after  an  ex- 
plosion has  occurred  in  which  fire-damp  or  coal-dust,  or 
both,  have  taken  part.  We  have  learnt  that  when  marsh 
gas  is  burnt  it  produces  carbon  dioxide  and  water  vapour, 
hence  we  should  expect  to  find  these  two  substances  in 
after-damp.  We  have  learnt  also  that  when  coal  burns  in 
plenty  of  air  it  forms  carbon  dioxide,  a  deficit  of  air  makes 
carbon  monoxide  liable  to  be  produced ;  hence  we  may  ex- 
pect to  find  both  these  gases  present  in  the  mine  after  an 
explosion.  Nitrogen  will  not  burn,  i.e.  it  cannot  be  used 
up  in  an  explosion  and  so  will  remain  in  the  air  untouched  ; 
but  unfortunately  nitrogen  does  not  help  the  life  of  a  living 
thing. 

The  after-damp  of  the  Usworth  Colliery  Explosion  of 
1888  had  the  following  composition: — 

Carbon  dioxide 
Carbon  monoxide    . 
Methane 
Oxygen  . 
Nitrogen 
Impurities 

lOO'OO 

After-damp  may  or  may  not  support  the  burning  of  a 
candle ;  this  depends  upon  the  amount  of  air  present.  It  is 
sure  to  be  dangerous  to  human  beings  on  account  of  the 
presence  in  it  of  carbon  monoxide. 

Black-damp, 

This  gas  will  extinguish  a  light  and  will  not  burn.  Up  to 
the  present  we  have  met  two  gases  which  behave  in  the 
same  way  as  black- damp  ;  they  are  carbon  dioxide  and 
nitrogen.  The  question  arises,  is  black-damp  a  different 
gas  from  these  two  or  is  it  a  mixture  of  them,  or  only  one 
of  them  ?  It  was  originally  thought  that  black-damp  con- 
sisted of  carbon  dioxide,  but  it  is  now  known,  if  unmixed 
with  air,  to  consist  of  carbon  dioxide  and  nitrogen.  The 


I2O          An  Introduction  to  Mining  Science. 

proportion  of  the  two  gases  vary  in  different  samples  of 
black-damp,  and  if  we  leave  out  of  consideration  any  air 
mixed  with  them,  then  the  following  figures  show  that  there 
is  always  much  nitrogen  present : — 

Nitrogen  varies  between  88  to  85  per  cent. 
Carbon  dioxide  varies  between  12  to  15  per  cent. 

Suppose  we  took  a  sample  of  pure  air  and  by  burning 
carbon  in  it  turned  all  the  oxygen  into  carbon  dioxide ; 
then  we  should  have  a  specimen  of  pure  black-damp  of  the 
following  composition  : — 

Nitrogen     .         .         .         .         -79  per  cent. 
Carbon  dioxide    .         .          .          .21          ,, 

If  we  left  in  10  per  cent  of  oxygen,  then  the  black-damp 
would  have  50  per  cent  of  air  in  it,  and  its  composition 
would  be : — 

Air    ......     50  per  cent. 

Carbon  dioxide  .         .  1 1         ,, 

Nitrogen    .  .     39        „ 

You  will  see  how  these  figures  are  arrived  at  after  reading 
the  following  paragraph. 

Ways  of  Stating  the  Composition  of  Damps, 

The  manner  of  stating  the  composition  of  the  damps 
which  are  mixtures  of  different  gases  is  worth  consider- 
ing. In  this  connexion  it  should  be  recalled  that  fresh 
air  contains  oxygen  and  nitrogen  in  the  proportions  of  four 
of  nitrogen  to  one  of  oxygen;  more  accurately  it  is  79  of 
the  former  to  21  of  the  latter,  but  the  simpler  numbers 
will  be  exact  enough.  It  is  therefore  plain  that  if  we  multi- 
ply the  amount  of  oxygen  in  a  gas  by  4  the  result  will  give 
the  amount  of  nitrogen,  and  by  addition  of  the  oxygen  and 
nitrogen  we  have  the  quantity  of  air  present  in  the  damp, 
or  gas  mixture. 

In  illustration  of  this  we  will  give  the  composition  of  a 
gas  mixture  from  a  freshly  hewn  sample  of  coal. 


The  Mine  Gases  known  as  Damps.  121 

Carbon  dioxide  . 
Methane     .... 
Nitrogen    .... 
Oxygen       .... 
Other  gases         .         .         . 

lOO'O  „ 

The  oxygen  and  nitrogen  form  a  certain  quantity  of  air, 
and  so  the  composition  may  be  written  as  follows : — 

Carbon  dioxide  .         .         i  *6  per  cent. 

Methane  ....  44-6         „ 

Nitrogen  .  .         .  9-5         ,, 

Air  .  .  44-0         „ 

Other  gases       .         .  -3         „ 

lOO'O  „ 

The  44  per  cent  of  air  is  obtained  in  this  way:  8-8 
x  4  =  35 '2  per  cent  of  nitrogen,  and  then  the  8*8  per  cent 
of  oxygen  added.  This  leaves  9-5  per  cent  of  nitrogen  in 
excess,  i.e.  above  the  amount  in  the  44  per  cent  of  air. 

The  analysis  of  the  air  from  a  return  airway  was  stated  in 
the  following  figures  : — 

Fire-damp         .  .         .         '5    per  cent. 

Oxygen     .         .  .          .19-5 

Carbon  dioxide  ..  ......       -75        „ 

Nitrogen  .     79-25 

This  analysis  does  not  in  a  plain  manner  tell  us  the 
amount  of  air  present,  it  may  be  calculated  in  the  manner 
described:  19-5  x  4  =  78  per  cent,  the  nitrogen  corre- 
sponding to  the  19*5  of  oxygen,  and  so  the  air  is  97*5  per 
cent,  i.e.  almost  pure  air.  The  composition  may  therefore 
be  written  : — 

Fire-damp         ...         '5  per  cent. 
Air                     ...     97-5 
Nitrogen            .          .         .1-25          „ 
Carbon  dioxide         ,         .         '75          ,, 


122  An  Introduction  to  Mining  Science. 

It  is  a  far  more  instructive  way  and  has  more  meaning 
than  the  first  one. 

As  black-damp  consists  of  carbon  dioxide  and  nitrogen 
the  analysis  might  be  written  thus  : — 

Fire-damp         .          .         .          -5  per  cent. 
Air  ....     97-5 

Black-damp      .         .          .        2'o         ,, 

In  this  case  the  name  fire-damp  means  methane,  and 
not  in  the  sense  used  in  the  analyses  on  page  107. 

The  composition  of  the  sample  of  after-damp  of  the 
Us  worth  Colliery  explosion  has  a  more  impressive  tale  to  tell 
if  we  write  it  as  follows  : — 

Air         .          .  .  .36-15  per  cent. 

Black-damp     .  .  .     52  '4.2  ,, 

Carbon  monoxide  .  .        2*48  „ 

Methane         .  .  .       8-68  „ 

Impurities       .  .  .         -27  ,, 

The  air  and  black -damp  are  calculated  as  shown  on 
pages  1 20  and  121. 

Practical  Application  to  Mining, 

Fire-damp,  called  by  the  miner  "  gas,"  is  usually  given 
off  steadily  from  the  coal  as  it  is  worked,  but  sometimes  an 
accumulation  is  tapped  and  the  gas  issues  forth  in  the  form 
of  a  "  blower  ". 

In  the  early  days  of  mining,  when  pits  were  shallow,  the 
fire-damp  found  its  way,  through  cracks  in  the  rocks,  to  the 
surface  and  was  seldom  found  in  the  workings  of  the  mine. 
As  the  top  seams  became  exhausted  and  pits  became  deeper 
it  was  confined  in  the  mine,  and  its  presence  was,  and  is 
to-day,  a  source  of  danger  to  the  miner. 

Before  the  introduction  of  the  safety  lamp  the  methods 
of  testing  for  and  removing  fire-damp  were  very  primitive.  In 
order  to  clear  the  workings  of  fire-damp,  the  ''fireman," 
wrapped  in  old  clothing  saturated  with  water  and  carrying 
a  lighted  taper  fixed  to  the  end  of  a  long  stick,  travelled 
round  the  mine  and  removed  the  gas  by  igniting  it  with  his 
taper.  Another  method  was  to  hang  a  naked  light  in  a 


The  Mine  Gases  known  as  Damps.  123 

place  where  gas  was  given  off,  and  by  burning  it  up  prevent 
its  accumulation. 

Fire-damp  is  detected  by  the  "  cap  "  or  halo  which  is 
formed  round  the  flame  of  the  candle  or  lamp.  The  cap 
is  best  seen  on  the  lowered  and  non-luminous  flame  of  the 
safety  lamp.  When  candles  were  used  the  observer  who 


FIG.  70. — Hurdle  sheet — front  view. 


FIG.  71. — 'Hurdle  sheet — side  view. 

wished  to  test  for  gas  had  to  place  his  hand  in  front  of  the 
flame  in  order  that  its  brightness  should  not  prevent  him 
seeing  the  cap. 

The  fire-damp  cap  is  caused  by  the  burning  of  the  particles 
of  gas  in  the  immediate  neighbourhood  of  the  flame.  When 
the  amount  of  gas  in  the  air  is  small  the  particles  are  a  long 
way  apart,  and  the  cap  is  very  faint  and  not  easily  seen  ;  but 


124  An  Introduction  to  Mining  Science, 

as  the  proportion  of  gas  increases  the  cap  becomes  larger 
and  more  clearly  defined.  If  the  proportion  of  gas  con- 
tinues to  increase  the  particles  become  so  close  together 
that  if  combustion  is  once  started  each  particle  will  ignite 
its  neighbour,  and  combustion  will  travel  through  the  mix- 
ture of  air  and  gas  without  any  further  help  from  the  initial 
source  of  heat.  This  is  called  explosion. 

Fire  damp  in  modern  mines  is  removed  by  diluting  it 
with  air  to  such  an  extent  that  it  ceases  to  be  dangerous. 
In  working  coal  by  the  Longwall  method  the  gate  roads 
along  which  the  coal  is  brought  to  the  main  roads  and  so 
to  the  pit  shaft,  are  made  of  sufficient  height  by  taking 
down  a  slab  of  roof.  This  is  called  "  ripping "  or 
"  brushing "  the  gate.  Fire-damp  often  accumulates  at 
the  face  of  this  ripping  and  may  be  removed  by  means  of  a 
"  hurdle  sheet "  which  conducts  air  up  into  the  gas  and  so 
clears  it  away. 

When  a  comparatively  large  accumulation  of  fire-damp  is 
found,  it  should  be  removed  in  layers  or  slices  as  shown  in 
Fig.  37,  Chapter  III,  page  62,  which  shows  how  the  gas  is 
removed  from  a  pair  of  headings  or  roads  driven  in  the 
solid  coal. 

Should  the  safety  lamp  become,  or  be  likely  to  become, 
extinguished  in  fire-damp,  it  is  both  foolish  and  dangerous  to 
go  forward  into  the  gas  without  light,  or  even  with  an  electric 
lamp.  Many  lives  have  been  lost  in  this  way  and  the 
practice  cannot  be  too  strongly  condemned. 

Black-damp, 

Black-damp  is  the  name  given  by  the  miner  to  the  gas 
which  is  not  inflammable  but  puts  out  the  light  of  a  candle 
or  lamp.  It  accumulates  in  old  workings,  and  when  a  fall 
of  the  barometer  takes  place  may  come  out  into  the  road- 
ways where  work  is  being  carried  on. 

When  mixed  with --air  it  is  detected  by  its  effect  on  the 
flame  of  a  candle  or  lamp,  which  burns  dimly  or  is  ex- 
tinguished according  to  the  proportion  of  gas  present. 

Carbon  dioxide  in  air  has  a  similar  effect  on  the  flame, 
and  the  miner  would  probably  be  unable  to  determine  by 
this  test  which  gas  was  present. 


The  Mine  Gases  known  as  Damps.  12$ 

It  is,  however,  important  to  notice  that  while  carbon 
dioxide  is  considerably  heavier  than  air  and  likely  to  collect 
in  low-lying  places,  black-damp  may  be  very  little  heavier 
than  air,  and  even  lighter. 

White-damp. 

White-damp  or  carbon  monoxide  is  formed  in  mines 
when  shots  are  fired,  when  explosions  of  fire-damp  or  coal- 
dust  and  air  take  place,  and  may  be  given  off  from  fires  due 
to  spontaneous  combustion  or  other  causes. 

It  is  a  very  poisonous  gas,  and  very  small  proportions  in 
air  are  dangerous. 

The  need  for  a  knowledge  of  its  properties,  behaviour, 
and  effect  on  men  may  be  better  realized  by  considering 
how  some  lives  have  been  lost  owing  to  its  presence  in  the 
mine. 

In  the  report  of  the  Inspector  of  Mines  for  Yorkshire  and 
the  North  Midlands,  1910,  an  account  is  given  of  an  acci- 
dent in  the  sinking  at  Thorne  Colliery,  near  Doncaster. 

A  round  of  fifteen  shots,  each  containing  i  J  Ib.  of  gelignite, 
was  fired  simultaneously  by  electricity.  The  men  returned 
to  work  almost  immediately — in  about  six  minutes — and 
although  no  fumes  or  smoke  were  visible  some  of  the  men 
were  affected  and  felt  ill ;  they  did  not  however  leave  work 
until  the  end  of  the  shift — three  hours  after  the  firing  of 
the  shots. 

On  reaching  home  several  of  the  men  became  seriously 
ill  and  one  of  them  died.  The  cause  of  death  was  carbon 
monoxide  poisoning,  and  there  was  also  some  irritation  by 
nitrous  fumes. 

Another  accident,  which  occurred  at  Langton  Colliery, 
Nottinghamshire,  is  described  in  the  same  report. 

A  very  small  heading  was  being  driven  to  make  com- 
munication with  another  road.  The  deputy  fired  a  charge 
of  Rippite  and  afterwards  examined  the  place.  He  detected 
no  danger,  and  a  skilled  miner  went  to  work  in  the  place 
alone.  About  fifteen  minutes  after  he  was  found  lying  dead 
near  the  face.  He  had  died  from  carbon  monoxide  poison- 
ing, and  probably  had  fainted  before  he  realized  that  he 
was  in  danger. 


126  An  Introduction  to  Mining  Science. 

It  is  very  difficult  to  detect  the  presence  of  carbon  mon- 
oxide, as  even  dangerous  quantities  have  no  appreciable 
effect  on  the  flame  of  a  safety  lamp.  The  only  practical 
method  of  detection  which  has  been  successfully  employed 
is  the  use  of  mice  or  small  birds  as  detectors.  They  suc- 
cumb to  the  poison  much  more  quickly  than  a  man  does, 
and  by  observing  their  symptoms  it  is  possible  to  determine 
the  presence  of  dangerous  quantities  of  the  gas  in  time  to 
make  a  safe  retreat. 

Dr.  Harger  has  recently  given  an  account l  of  a  method 
of  detecting  carbon  monoxide  by  the  reduction  of  iodine 
pentoxide — a  chemical  method.  The  heat  necessary  to 
start  the  reaction — about  170°  Centigrade — is  found  in  the 
safety  lamp  between  the  top  of  the  gauze  and  the  bonnet. 

The  following  requirements  of  the  Coal  Mines  Act  relat- 
ing to  gases  are  very  important : — 

"  A  working  place  must  be  considered  dangerous  if  the 
percentage  of  inflammable  gas  in  the  general  body  of  air  is 
found  to  be  2-J  per  cent  or  upwards,  or  if  in  a  part  of  a 
mine  worked  with  naked  lights,  ij  per  cent. 

"If  a  workman  discovers  the  presence  of  inflammable 
gas  in  his  working  place,  he  shall  immediately  withdraw 
therefrom  and  inform  the  deputy. 

"  Two  or  more  small  birds  or  mice  for  testing  for  carbon 
monoxide  shall  be  provided  and  maintained  at  every  mine 
which  maintains  a  rescue  brigade  or  brigades." 

QUESTIONS. 

1.  In  1914  there  were  explosions  of  marsh  gas  in  several  houses 
at  Bradford,  and  in  the  report  it  stated,  "  the  gas  was  attracted  by  open 
fires"  in  grates.      Can  you    offer  any  other  explanation  of  the   gas 
moving  towards  the  fire-grates  ? 

2.  A  sample  of  air  from  the  return  airway  of  a  pit  gave  the  follow- 
ing results  on  analysis  : — 

Pure  air        ....      90-5  per  cent. 
Black-damp   ....       g-o        ,, 
Fire-damp      ....         *5         ., 

Write  down  the  names  of  the  gases  present. 

3.  Arrange  the  gases  found  in  mines  in  two  groups  :  (i)  combust- 
ible ;  (2)  non-combustible. 

1  "  Trans.  Inst.  Mng.  Eng.,"  Vol.  XL VII. 


The  Mine  Gases  known  as  Damps.  127 

4.  A  match  may  be  ignited  in  the  air  without  exploding  or  setting 
it  on  fire.     What  does  this  prove  about  the  air  and  the  gases  com- 
posing it  ? 

5.  Name  the  gases  of  the  mine  which  have  a  smell.     What  are 
the  advantages  of  a  gas  possessing  a  smell  ? 

6.  Which  gas  is  most  likely  to  be  ignited  i  in  a  mine  by  a  spark  ? 
How  are  sparks  likely  to  be  produced  ? 

7.  Mention  the  gases  found  in  the  mine  which  are  (i)  necessary 
for  health  and  life ;  (2)  injurious  to  health  and  life.     Are  any  of  these 
gases  found  in  an  ordinary  living-room  ? 

8.  What  gas  is  added  to  the  air  by  breathing  ?     How  is  the  same 
gas  produced  in  a  mine  ? 

9.  What  is  the  difference  between  black-damp  and  choke-damp  ? 
How  could  you  prove  by  experiment  they  are  different  gases  ? 

10.  Are  there  any  gases  present  in  coal  gas  which  are  not  found  in 
a  mine  ?     If  so,  mention  them. 

11.  On  page  136  it  is  said  a  mixture  of  air  and  coal  gas,  containing 
6*5  per  cent  or  less  of  the  latter,  will  not  burn.     Yet  "  gas  caps"  are 
often  shown  containing  less  than  6-5  per  cent  of  coal  gas.     Can  you 
reconcile  these  two  facts  ? 

12.  How  has  it  been   proved    that    black-damp    contains    carbon 
dioxide  ? 

13.  Distinguish  between  marsh  gas  and  fire-damp.     If  some  marsh 
gas  escaped  into  the  air  would  you  call  the  mixture  fire-damp  ? 

14.  Can  you  give  reasons  why  the  various  damps  have  one  of  the 
following  prefixes  :  black,  white,  choke,  after,  fire,  and  stink  ? 

15.  What  conditions  decide  that  miners  should  be  withdrawn  from 
their  working  place  ?     What  should  be  done  when  they  have  with- 
drawn ? 

16.  Burnt  and  injured  people  are  not  a  very  large  proportion  of  the 
killed  in  colliery  explosions  ;  how  do  you  account  for  the  large  propor- 
tion otherwise  killed  ? 


CHAPTER  VII. 

SUBSTANCES  WHICH,  MIXED  WITH  AIR,  FORM 
EXPLOSIVE  MIXTURES. 

EXPLOSIONS  are  fairly  well  known  to  everybody,  but  it  is 
not  as  well  known  that  air  must  get  mixed  with  the  gas  or 
vapour  causing  the  explosion  before  one  is  possible. 

Recall  any  information  you  possess  on  colliery  explosions  ; 
on  gas  explosions  in  houses ;  on  explosions  due  to  liquids 
giving  off  inflammable  vapours ;  on  explosions  used  as  the 
driving  force,  in  the  engine  of  a  motor-car,  or  motor-cycle 
or  any  engine  driven  by  gas,  petrol,  or  oil. 

The  effects  of  well-known  explosions  are  better  known 
than  their  causes  ;  shattering  walls  and  demolishing  buildings 
are  the  common  accompaniment  of  "  good  "  explosions. 
Small  explosions  or  "  bangs"  are  known  to  most  people  who 
have  experience  of  any  form  of  atmospheric  burner.  These 
explosions,  due  to  mixtures  of  air  and  gas,  or  vapour,  must 
not  be  confused  with  those  occurring  in  the  use  of  ex- 
plosives, which  are  generally  solid  substances  capable  of 
exploding  independently  of  the  presence  of  air,  e.g.  bombs 
dropped  from  aeroplanes. 

Experience. 

The  gas-stove  burner,  the  incandescent  gas  burner,  ring-stove 
burners  used  in  workshops,  are  all  examples  of  atmospheric 
burners  :  those  where  gas  and  air  mix.  If  there  be  any  burners 
of  the  foregoing  type  in  your  school  or  home  search  for  the  gas 
nipple,  and  note  close  by  it  is  an  inlet  for  air.  The  gas  leaving  the 
nipple  rushes  up  a  tube  leading  to  the  burner  and  the  air  follows  ; 
as  they  go  along  it  they  mix. 

In  each  case  we  may  know  by  experience  that  in  lighting 
such  burners  there  are  "  pops  "  or  explosions  in  the  tube,  and 

128 


Substances  which  form  Explosive  Mixtures.       129 

the  gas  at  the  nipple  is  found  to  be  burning.  This  is  the 
commonest  and  least  dangerous  kind  of  explosion  ;  it  shatters 
nothing  because  the  exploding  gas  is  not  shut  up,  but  its 
exploding  force  disturbs  the  atmosphere,  and  in  so  doing 
makes  a  sound. 

It  is  important  to  notice  that  petrol,  gas,  and  oil  may  all 
burn  silently  as  a  flame  when  giving  light.  This  is  because 
particles  of  the  flame  keep  well  together  and  are  not  mixed 
with  air.  Where  gas  particles  are  not  mixed  with  air  each 
particle  of  the  gas  or  vapour  has  to  wait  its  turn  until  it  gets 
on  the  edge  or  on  the  faces  of  the  flame  so  as  to  get  air  to 
burn  it ;  i.e.  to  take  all  the  light  and  heat-giving  power  out 
of  it.  As  soon  as  the  particles  of  a  gas  or  vapour  get 
intimately  mixed  with  air,  in  a  closed  space,  there  is  a 
greater  chance  of  an  explosion. 

Experiment. 

Take  two  pellets  of  cotton-wool  and  soak  each  with  ether,  or 
petrol,  or  benzoline.  Place  one  piece  in  a  porcelain  dish  and  the 
other  in  a  glass  cylinder.  Shake  the  one  in  the  cylinder  so  as  to 
mix  the  vapour  and  air  ;  have  a  glass  cover  on  the  cylinder. 
Apply  a  light  to  each,  in  the  latter  case  with  caution. 

Compare  and  explain  the  burning  of  the  ether  in  each  case. 

The  porcelain  dish  is  a  very  open  vessel  and  the  burning 
will  be  ordinary  combustion,  but  in  the  glass  cylinder  there 
may  be  a  slight  "  pop  "  on  applying  the  light.  The  vapour 
in  the  cylinder  is  more  confined  than  any  given  off  in  the 
porcelain  dish,  and  this,  taken  in  conjunction  with  its 
firing  instantaneously,  gives  a  small  explosion.  Confining  a 
combustible  vapour  mixed  with  air  makes  it  dangerous  when 
a  light  is  applied.  The  following  experiment  will  give  a 
better  illustration  of  the  effects  of  firing  a  vapour  in  a  less 
open  vessel. 

Experiment, 

Take  a  flask,  or  a  bottle,  or  other  vessel  with  a  neck,  and  place 
in  it  a  drop  or  two  of  petrol  or  ether.  Warm  the  liquid  slightly 
for  vaporizing  it.  Drop  a  lighted  match  into  the  mixture 
of  vapour  and  air,  notice  the  explosion.  If  one  or  two  drops 
fail  try  a  few  more  drops,  but  increase  by  one  at  a  time. 

9 


130          An  Introduction  to  Mining  Science. 

This  experiment  brings  us  in  contact  with  the  fact  that 
petrol  and  air  will  explode  when  ignited,  and  the  "  pop  " 
obtained  in  the  experiment  tells  us  that  gases  are  forced 
up  the  neck  of  the  vessel.  A  valve  on  the  top  of  the  neck 
could  be  lifted  up ;  it  would  fall  down  after  explosion. 
Such  an  idea  brings  us  face  to  face  with  using  petrol  and 
air  as  a  motive  power. 

The  fact  that  petrol  and  air  easily  form  an  explosive 
mixture  has  led  to  the  making  of  the  petrol  engine.  The 
explosion  of  the  mixture  in  that  part  of  the  engine  called 
the  cylinder — the  envelope  or  jacket  in  which  the  piston 
moves — leads  to  the  forcing  of  the  piston  along  and  finally 
the  turning  of  the  wheels. 


~ 

r 

e 

FIG.  72. — Diagram  of  the  cylinder  of  an  engine. 

The  movable  piston-rod  is  shown  at  P ;  it  works  inside  the 
cylinder  C.  The  gas  and  air  intake  is  shown  at  A.  The  prin- 
ciple is  the  same  in  the  gas  engine  and  petrol  motor.  An  ex- 
plosive mixture  of  either  gas,  or  petrol  vapour,  and  air  is 
injected  or  sucked  into  the  cylinder  along  A,  and  exploded 
usually  by  an  electric  spark.  The  explosion,  which  is  very 
rapid  combustion,  results  in  the  cylinder  being  filled  with 
gases  at  a  high  temperature,  and  the  piston  is  driven  forward. 
Then  the  piston  returns  and  the  gases  are  expelled  from  the 
cylinder.  This  occurs  very  frequently,  so  the  engine  is  set 
working,  the  wheels  turned,  and  the  car  propelled.  The 
maximum  force  is  got  with  a  mixture  consisting  of — 

2  *6  parts  of  petrol  vapour. 
97-4     „       „  air. 

Above  2  -6  parts  of  petrol  vapour,  and  therefore  a  decrease 
in  the  parts  of  air,  the  force  of  the  explosion  diminishes ;  when 
it  has  become  5  parts  of  petrol  vapour  and  95  parts  of  air  it 


Substances  which  form  Explosive  Mixtures.       131 

burns  quietly.  It  is  therefore  important  in  such  engines  that 
the  correct  proportions  of  air  and  petrol  vapour  should  be 
mixed. 

One  gallon  of  petrol  makes  1500  cubic  feet  of  mixed  air  and 
petrol  vapour. 

Notice  that  on  these  explosions  taking  place  in  a  cylinder 
there  is  a  movable  piston  which  takes  the  force  of  the  ex- 
plosion ;  if  it  were  a  fixed  thing,  then  the  force  would  be  felt 
all  over  the  cylinder  and  a  shattering  of  its  walls  might  occur. 

Experience. 

If  a  bottle  of  benzoline  (or  benzine)  is  bought  from  the 
chemist's  it  will  be  labelled  "  Highly  Inflammable,"  and  further 
the  label  will  tell  you  not  to  bring  a  light  near  nor  to  use  it  too 
near  a  fire. 

Why?  The  boiling-point  of  Benzoline  lies  between  70° 
C.  and  90°  C.  ;  it  is  therefore  a  very  low  one,  and  inflam- 
mable vapour  is  easily  given  off.  If  air  got  access  to  the 
bottle  a  mixture  of  air  and  benzoline  vapour  would  be 
formed  ;  then  a  light  would  explode  the  mixture,  scattering 
the  bottle  liquid,  and  probably  burning  the  holder.  Benzoline 
is  a  near  relative  of  petrol  and  petroleum ;  the  latter  is  the 
parent  substance  of  both. 

Alliinflammable  liquids  such  as  petrol,  gasoline,  petroleum 
spirit,  benzoline,  etc.,  have  to  be  handled  very  carefully,  as  at 
the  ordinary  temperature  of  the  air  they  give  off  inflammable 
vapours.  If  a  light  be  brought  near  it  may  cause  their 
vapour  to  ignite ;  this  danger  is  warded  against  by  the  special 
precautions  taken  by  dealers  and  railway  companies  in  the 
storage  and  transit  of  these  liquids.  In  no  circumstances 
is  a  naked  light  to  be  allowed  in  the  store-rooms,  or  to  ap- 
proach the  storage  tanks  situate  in  the  open  air. 

The  most  volatile  relative  of  petrol  called  gasoline,  which 
boils  between  50°  C.  and  60°  C.,  would  be  extremely  explo- 
sive if  mixed  with  air  and  a  light  applied. 

The  easier  a  substance  becomes  a  vapour  and  mixes  with 
air  the  more  dangerous  it  is  owing  to  the  possibility  of  ex- 
plosions being  produced. 

9* 


132          An  Introduction  to  Mining  Science. 

If  we  arrange  the  four  mentioned  liquids  according  to  the 
lightness  of  their  vapours,  the  following  table  is  got : — 

Boiling-points. 

Gasoline  (lightest)     .  .       5o°-6o°   C. 

Benzoline  or  benzine        .         .        7o°-90°  C. 
Petrol  .  .       90°- 1 30°  C. 

Petroleum  (heaviest)        .         .     i5o°-3oo°C. 

and  we  at  once  perceive  from  our  experience  and  know- 
ledge of  these  liquids  that  the  lightest  vapour  belongs  to 
the  liquid  with  the  lowest  boiling-point.  The  lighter  the 
vapour  the  more  rapidly  its  particles  mix  with  air  and  the 
more  likely  an  explosion  may  result  if  it  be  an  inflammable 
vapour.  All  the  foregoing  substances  are  obtained  from 
the  natural  mixture  called  crude  petroleum  after  it  has  been 
brought  from  the  oil  wells.  It  is,  when  first  obtained,  a 
thick  syrupy  liquid,  in  appearance  not  unlike  the  coarsest 
kind  of  treacle,  varying  in  colour  from  brown  to  nearly 
black  ;  it  has  a  rather  unpleasant  odour. 

This  crude  petroleum  is  refined  as  coarse  treacle  is,  that 
is,  separated  into  different  parts  ;  four  of  these/parts  we  have 
already  considered. 

Gases  in  Crude  Petroleum. 

It  is  a  fact  that  there  are  substances  in  crude  petroleum 
with  lower  boiling-points  than  those  we  have  considered ; 
these  are  gases ;  the  temperature  of  the  air  keeps  them  so 
because  its  temperature  is  too  high  to  allow  them  to  be- 
come liquids.  There  are  gases  in  American  crude  petroleum 
which  come  out  of  the  oil  in  much  the  same  way  as  car- 
bonic acid  gas  comes  out  of  an  effervescing  drink.  These 
gases,  one  of  which  is  marsh  gas  or  fire-damp,  are  artificially 
liquefied  by  cold  and  pressure  and  sold  for  industrial 
purposes,  such  as  lighting,  where  there  is  no  other  gas  supply 
possible. 

Solid  Substances  in  Petroleum. 

Vaseline  and  paraffin  wax  are  two  substances  which  be- 
long to  the  petroleum  family  :  crude  petroleum  is  their  parent. 
It  may  be  remarked  that  these  two  substances  are  not  ex- 


Substances  which  form  Explosive  Mixtures.       133 

plosive,  which  is  true,  and  the  reason  is  not  far  to  seek. 
They  are  solid  or  semi-solid  substances  whose  boiling  and 
melting-points  are  so  far  above  the  ordinary  temperature 
of  the  air  that  they  do  not  even  give  off  any  vapour.  There 
is  therefore  no  chance  for  a  mixture  of  vapour  and  air  to 
be  formed.  If  either  be  highly  heated  so  as  to  be  vaporized 
the  vapour  which  comes,  off  is  combustible. 

In  separating  the  various  constituents  of  petroleum  from 
one  another  heat  is  employed,  and  those  substances  which 
are  naturally  gases  easily  leave  the  liquid ;  then  those  sub- 
stances which  are  naturally  liquids  boil  away,  the  two 
substances,  vaseline  and  paraffin,  being  left  behind.  The 
use  of  heat  in  the  separation  of  the  petroleum  chars  part 
of  the  constituents,  and  this  is  left  behind  in  the  vessel  as 
coke  ;  it  is  used  for  making  electric  light  carbons. 

A  Further  Note  on  Petroleum, 

The  first  discovery  of  petroleum  in  quantity  was  made 
in  a  disused  mine  in  Derbyshire  in  1847  as  a  spring  of  the 
oil.  This  spring  is  now  exhausted. 

In  1848  the  oil  began  to  be  made  artificially  by  heating 
and  distilling  cannel  coal. 

In  1 86 1  petroleum  was  found  in  Pennsylvania  in  a  well 
artificially  bored,  the  well  giving  at  least  100,000  gallons  a 
day.  Since  the  foregoing  date  petroleum  has  been  found 
in  different  parts  of  the  world. 

Now  it  is  important  to  notice  that  these  sources  are 
either  intimately  connected  with  the  under  parts  of  the 
earth's  surface,  or  with  coal.  It  appears  then  that  as  well 
as  the  earth  providing  us  with  a  solid  combustible  material 
called  coal  which  comes  from  various  depths  and  gives  off 
inflammable  gas,  it  .also  provides  us  with  a  combustible 
liquid  called  petroleum.  Both  give  off  the  same  inflammable 
gas  known  as  marsh  gas  or  fire-damp.  Moreover,  the 
making  of  petroleum  from  cannel  coal,  helps  to  show  how 
related  coal  and  petroleum  are,  and  the  presence  of  fire- 
damp in  both  helps  to  further  emphasize  the  relationship. 

If  then  we  keep  before  our  minds  the  inflammability  and 
the  ease  with  which  some  of  the  constituents  of  petroleum 


134  An  Introduction  to  Mining  Science, 

explode,  we  shall  recognize  the  danger  of  explosion  from  the 
gases  which  come  out  of  coal. 

Some  Simple  Explosions, 
Experiment, 

Make  a  V-shaped  cardboard  trough  about  1 8  inches  long  £ 
and  fix  one  end  of  it  higher  than  the  other  ;  at  the  lower 
end  place  a  lighted  candle.  From  the  higher  end  pour  the 
vapour  of  ether  or  petrol  down  the  trough  ;  this  is  conveniently 
done  by  placing  a  small  quantity  of  the  liquid  in  a  beaker ;  it 
vaporizes  and  flows  as  a  liquid  would  down  the  trough. 

It  is  an  advantage  to  perform  the  experiment  in  a  place  free 
from  strong  draughts. 

This  experiment  illustrates  "  striking  back,"  i.e.  the  passage 
of  a  flame  backwards  to  the  source  of  supply.  The  vapour 
flows  down  the  trough  and  mixes  with  air;  the  mixture 
thus  formed  touches  the  light  of  the  candle  and  the  flame 
of  the  burning  ether  runs  up  the  trough  to  the  beaker, 
igniting  the  ether  in  it.  This  is  one  reason  why  there 
should  be  very  little  ether  in  the  beaker.  The  rate  at  which 
the  flame  travels  up  the  trough  should  be  noted;  it  is 
practically  instantaneous. 

If  gas  from  a  blow-hole  had  been  filling  a  roadway  in 
a  mine  and  becoming  mixed  with  air,  and  if  a  light  were 
applied  to  it  or  the  mixture  flowed  towards  a  light  at  the 
end  far  away  from  the  blow-hole,  the  flame  would  strike 
back  to  the  blow-hole  and  light  the  issuing  gas. 

Experience. 

You  have  no  doubt  lit  a  gas  by  holding  a  match  several  inches 
away  from  the  issuing  gas.  The  mixture  near  the  lighted  match 
takes  fire  and  then  the  flame  strikes  down  to  the  gas  nipple. 

The  Bunsen  Burner  and  a  Mixture  of  Gas  and  Air, 

Passing  up  the  tube  of  the  Bunsen  Burner  when  the  holes 
are  open  is  a  mixture  of  coal  gas  and  air ;  at  the  top  it  burns 
very  quietly  when  lighted.  Yet  we  know  that  if  there  is  any 
escape  of  gas  in  a  room,  which  of  course  mixes  with  the 
air  of  the  room,  generally  the  introduction  of  a  light  leads 
to  a  more  or  less  violent  explosion. 


Substances  which  form  Explosive  Mixtures.       135 

Experiment. 

Turn  down  a  lighted  Bunsen  gently  so  as  to  produce  a  small 
flame  and  see  if  the  flame  strikes  back  to  the  gas  nipple.  By 
altering  the  "  air  intake  "  when  a  full  flame  is  burning,  a  point  is 
reached  when  the  flame  makes  a  faint  roar.  "  Striking  back  " 
and  "  roaring  "  both  illustrate  explosions. 

Roaring  consists  of  a  succession  of  very  faint  "  pops  " 
due  to  alteration  of  the  air  supply.  The  place  where 
"  roaring  "  occurs  is  where  the  flame  and  inner  cone  of 
mixed  air  and  gas  come  together,  it  may  be  easily  seen  as  a 
troubled  region  in  the  flame.  Diminishing  the  air  supply 
makes  the  mixture  richer  in  coal  gas,  and  some  of  this 
mixture  arrives  at  the  hot  inner  surface  of  flame,  ignites  and 
"  pops  ". 

The  "  striking  back  "  of  the  Bunsen  flame  is  well  worth 
noticing,  because  it  is  similar  to  the  propagation  of  an  ex- 
plosion. As  the  burner  is  turned  down  the  speed  of  the 
gas  rushing  up  the  tube  is  checked,  and  as  the  flame  is  kept 
at  the  top  of  the  tube  by  the  speed  of  theuprushing  mixture 
of  gas  and  air,  an  opportunity  is  afforded  to  the  flame  to 
travel  through  the  mixture  of  air  and  gas  in  the  tube  and 
so  explode  it.  The  flame  of  the  explosion  ignites  the  gas 
issuing  from  the  gas  jet  at  the  bottom  of  the  tube. 


Experiment. 

Take  a  gas  cylinder  and  trough  of  water  and  fill  the  cylinder 
with  the  following  parts  of  coal  gas  and  air  : — 

(1)  iandf. 

(2)  TV  and  H- 

(3)  i  and  6. 

The  divisions  of  the  cylinder  may  be  made  with  gum  paper. 

The  cylinder  must  be  filled  with  water  and  the  gas  tube  held 
under  its  mouth  for  collecting  the  gas  ;  it  will  be  necessary  to 
have  the  open  end  of  the  gas  tube  only  an  inch  or  so  below  the 
water  surface  in  the  trough  for  the  gas  to  flow  out.  Withdraw 
the  gas  tube  from  under  the  cylinder  when  the  latter  has  filled 
to  the  required  amount.  Air  may  then  be  let  carefully  in  by 
bringing  the  mouth  of  the  cylinder  slowly  through  the  water 
surface, 


136  An  Introduction  to  Mining  Science. 

Apply  a  light  to  each  cylinder.  Notice  if  (i)  burns  quietly, 
(2)  with  difficulty,  (3)  with  explosive  effects,  the  flame  travelling 
slowly  down  the  jar. 

The  composition  of  the  mixtures  of  gas  and  air  can  easily 
be  put  as  percentages  by  stating  the  amounts  as  parts  of  a 
hundred,  i.e.  the  number  of  cubic  inches  or  feet  of  each  in 
100  cubic  inches  or  feet  of  the  mixture. 

The  proportions  of  gas  and  air  stated  as  percentages  are 
respectively:  (i)  33^  and  66f  ;  (2)  8J  and  Qif;  (3)  14? 
and  85!.  Compare  these  and  the  results  obtained  in  the 
experiments,  with  the  following  statements. 

The  following  mixtures  will  behave  as  stated : — 

Mixture.  Will  not  Burn.         Burns  Gently. 

Coal  gas  6-5  25 

Air  .     93-5  75 

lOO'O  IOO 

An  amount  of  gas  represented  by  any  number  between 
6-5  and  25  mixed  with  air  will  explode  more  or  less  violently, 
e.g.  the  following  mixture  : — 

Coal  gas         14-3 

Air  857 

100*0 

This  percentage  as  a  matter  of  fact  gives  the  most 
violent  explosion.  Less  than  6-5  will  not  burn,  more  than 
25  burns  gently. 

These  experiments  on  the  difference  in  the  behaviour 
of  mixtures  of  air  and  coal  gas  bring  out  the  fact  that  all 
mixtures  of  coal  gas  and  air  will  not  explode  ;  their  exploding 
depends  upon  the  amounts  of  air  and  coal  gas  mixed  to- 
gether. 

The  figures  and  facts  should  help  us  to  explain  how 
it  is  that  explosions  produced  in  houses  by  the  searching 
for  a  gas  escape  with  a  light  differ  in  their  effects.  Various 
proportions  of  gas  and  air  behave  in  different  ways,  and  so 
the  searcher  may  either  be  lucky  or  unlucky  enough  to  find 
a  gently  burning,  an  explosive,  or  a  non-burning  mixture. 

Compare  the  foregoing  figures  and  facts  with  those  given 
on  p.  107,  on  mixtures  of  air  and  marsh  gas. 


Substances  zvhich  form  Explosive  Mixtures.       137 

The  foregoing  experiments  and  facts  show  that  great 
dilution  of  an  inflammable  gas  with  air  destroys  the  power 
of  inflammability  of  coal  gas  or  marsh  gas.  Therefore,  in 
mines  dilution  with  air  may  tend  to  diminish  the  chances  of 
an  explosion,  and  dilution  with  a  flowing  current  of  air  will 
result  in  clearing  out  objectionable  gases  which  are  not 
inflammable  and  yet  very  injurious  to  human  beings. 

Dilution. 

Dilution  of  a  liquid  is  very  well  known,  and  is  often  per- 
formed on  account  of  its  being  too  strong  for  any  particular 
purpose.  The  dilution  is  generally  done  by  adding  water, 
owing  to  its  not  having  that  particular  property  of  the  liquid 
which  undergoes  dilution. 

Water  is  widely  used  for  diluting  and  carrying  away 
purposes  in  public  drains;  it  is  here  a  cleansing  current. 
It  is  very  much  the  same  as  the  cleansing  effect  of  a  river 
in  flood,  which  sweeps  forward  all  the  ill-smelling  deposits 
formed  on  its  banks  and  dilutes  the  objectionable  liquids 
poured  into  it  by  streams  from  manufacturing  districts. 

Experience. 

Too  strong  tea  is  diluted  by  hot  water,  or  too  sweet  a  liquid 
by  the  addition  of  an  unsweetened  liquid.  Too  strong  a  tobacco 
is  diluted  by  its  being  mixed  with  a  mild  kind. 

A  stuffy  hall,  room,  or  railway  carriage  has  its  ventilators 
opened  to  dilute  the  foul  inside  air. 

The  foregoing  therefore  shows  dilution  applied  to  liquids, 
solids,  and  gases;  it  is  performed  to  tone  down  some  ob- 
jectionable feature  of  a  substance. 

Experiment. 

Take  a  porcelain  dish  and  place  in  it  a  spoonful  of  methylated 
spirit,  ignite  it  and  then  put  out  the  flame  by  covering  the  dish. 
Add  a  spoonful  of  water  to  the  spirit,  stir,  and  try  to  ignite  ;  if 
it  ignites  add  further  small  quantities  until  it  ceases  to  ignite. 

The  power  of  inflammability  is  gradually  toned  down  and 
finally  destroyed. 

The    passage    of  large    volumes  of  air  through  the  pit 


138  An  Introduction  to  Mining  Science. 

dilutes  all  the  obnoxious,  injurious,  and  inflammable  gases 
produced  or  found  therein,  and  after  their  dilution  the 
ventilating  current  carries  them  out  of  the  mine.  Where 
parts  of  the  ventilating  current  are  moving  slowly,  as  at 
the  coal-face,  the  health-destroying  gases  and  explosion- 
producing  ones  are  mixing  with  it  and  become  so  dilute 
that  their  power  for  evil  is  much  diminished  if  not  actually 
destroyed. 

Dilution  should  be  brought  about  as  soon  as  you  find 
there  is  an  escape  of  gas  in  your  house  ;  open  all  doors  and 
windows  so  that  air  can  come  in,  dilute  it,  and  carry  it 
out  for  further  dilution  in  the  atmosphere.  In  the  room 
as  in  the  pit  the  first  step  is  to  dilute  an  objectionable  gas 
or  gases,  but  the  healthiest  way  is  to  clear  it  out  completely. 

Practical  Application  to   Mining, 

Probably  the  first  recorded  colliery  explosion  occurred 
early  in  the  seventeenth  century  and  caused  the  death  of 
one  man. 

Since  that  time  explosions  have  been  many  and  the 
number  of  lives  lost  from  this  cause  has  been  very  great 
indeed. 

The  majority  of  colliery  explosions  are  small  ones,  causing 
the  loss  of  few  lives  individually  but  mounting  up  to  large 
numbers  in  the  aggregate. 

Occasionally  a  disaster  of  great  magnitude  occurs  such 
as  the  Sengenydd  explosion,  which  took  place  on  14 
October,  1913,  and  in  which  440  men  lost  their  lives. 

The  average  death  rate  from  explosions  of  fire-damp  and 
coal  dust  in  all  mines  under  the  Coal  and  Metalliferous 
Mines  Regulation  Acts,  during  the  ten  years  from  1902  to 
1911,  was  '165  per  1000  persons  employed. 

In  1913  the  number  of  deaths  from  colliery  explosions 
in  mines  under  the  Coal  Mines  Regulations  Act  was  462, 
and  the  number  of  persons  injured  150. 

Colliery  exp'osions  may  be  divided  into  two  classes : — 

i.  Purely  fire-damp  explosions,  which  are  usually 
limited  in  extent  and  cause  comparatively  little  damage. 

The  Whitehaven  Colliery  explosion  of  1882  is  perhaps 


Substances  zuhich  form  Explosive  Mixtures.     1 39 

the  most  considerable  explosion  of  fire-damp  and  air  re- 
corded in  this  country. 

It  was  estimated  that  the  quantity  of  mixture  exploded 
amounted  to  about  32,800  cubic  feet,  yet  the  damage  done 
was  not  great  and  the  force  of  the  explosion  did  not  extend 
far  beyond  the  district  in  which  it  occurred. 

2.  Explosions  in  which  coal  dust  takes  part.  These 
often  travel  great  distances,  causing  enormous  damage  and 
the  loss  of  many  lives. 

It  was  not  until  early  in  the  nineteenth  century  that  coal 
dust  was  suspected  of  having  any  influence  on  colliery  ex- 
plosions, but  since  then  a  great  many  experiments  have 
been  made  with  a  view  to  finding  out  the  magnitude  of  the 
part  played  by  coal  dust. 

In  1908-9  the  British  Coal  Dust  Experiments,  con- 
ducted by  the  committee  appointed  by  the  Mining 
Association  of  Great  Britain,  were  carried  out  at  Altofts, 
Yorkshire.  The  experimental  gallery  was  designed  to  re- 
semble as  far  as  possible  the  conditions  of  the  mine.  It 
consisted  of  an  "  intake  "  and  "  return  ".  The  intake  was 
7  feet  6  inches  in  diameter  with  a  concreted  roadway  along 
which  ran  a  line  of  rails.  The  return  was  6  feet  in  diameter 
and  zig-zag  in  form. 

A  quantity  of  50,000  cubic  feet  of  air  per  minute  passed 
along  the  gallery  during  an  experiment.  The  quantity  of 
coal  dust  employed  was  i  Ib.  per  linear  foot,  or  0*4  oz.  per 
cubic  foot  of  air  space.  The  dust  was  usually  ignited  by 
firing  a  charge  of  24  oz.  of  blasting  powder  from  an  iron 
cannon  of  2 -inch  bore,  stemmed  with  8  inches  of  dry  clay. 

These  experiments  definitely  established  the  fact  that 
coal  dust,  in  the  complete  absence  of  fire-damp,  is  explosive 
when  raised  as  a  cloud  in  air  and  ignited. 


Cause  and  Prevention  of  Explosions, 

Many  explosions  have  been  caused  by  naked  lights,  de- 
fective lamps,  and  shot  firing,  but  other  causes,  such  as  the 
sparking  of  electrical  machinery  and  electric  bells  are  on  re- 
cord. Coal-dust  explosions  may  be  initiated  by  a  blown-out 


140          An  Introduction  to  Mining  Science. 

shot,  or  a  comparatively  small  explosion  of  fire-damp  may 
develop  into  a  dust  explosion  on  a  large  scale. 

Many  explosions  have  been  caused  by  ignorance  or  care- 
lessness on  the  part  of  workmen,  and  there  appears  little 
doubt  that  if  the  regulations  laid  down  in  the  Coal  Mines 
Act  were  thoroughly  understood  and  carried  out,  the  number 
of  explosions  would  be  greatly  reduced.  A  few  extracts  from 
inspectors'  reports  may  help  to  make  this  clear. 

"  On  a  Sunday  night  the  three  deceased  men,  before  enter- 
ing the  safety  lamp  area,  voluntarily  gave  up  matches  and 
cigarettes  to  the  fireman  of  the  section,  who  did  not  for  this 
reason  search  them  as  he  should  have  done.  They  proceeded 
to  their  level  working-place,  but  left  it  at  once  and  went  to 
work  in  the  rising  place  of  a  neighbour  who  was  absent,  and 
to  which  they  had  no  right  to  go,  and  in  which  the  fireman 
had  told  them  gas  had  accumulated  and  was  present. 

"...  They  were  working  with  C.E.A.G.  electric  lamps, 
and  in  spite  of  the  fact  that  they  had  been  told  of  gas,  they 
had  secreted  matches  and  cigarettes  in  the  folds  of  their  caps 
and  had  begun  to  smoke,  as  burnt  cigarettes  and  matches  were 
afterwards  found  in  the  working  face,  with  the  result  that  the 
accumulation  of  gas  was  ignited  and  an  explosion  occurred, 
and  so  seriously  burned  them  all  that  they  died  shortly  after- 
wards." 

"  A  collier  was  burnt  by  the  ignition  of  fire-damp  by  his 
naked  light  on  going  into  a  place  which  was  fenced  off,  in 
order  to  get  a  boring  machine." 

"  A  fireman  was  burnt  by  an  ignition  of  fire-damp  ignited 
by  a  match  which  he  struck  to  relight  a  safety  lamp." 

The  danger  from  coal  dust  may  be  reduced  by  using  dust- 
proof  tubs,  and  so  preventing  to  some  extent  the  deposition 
of  dust ;  by  removing  the  screens  a  considerable  distance 
from  the  shaft,  or  so  collecting  the  dust  made  at  the  screens 
that  it  is  prevented  from  going  down  the  shaft ;  by  cleaning  up 
and  preventing  accumulations  of  dust  in  haulage  roads,  and  by 
the  application  of  water  or  incombustible  dust. 

In  the  Fifth  Report  of  the  Explosions  in  Mines  Committee 
it  is  stated  that  a  i  to  i  mixture  of  coal  dust  and  incombust- 
ible dust  could  not  be  fired  by  a  charge  of  24  oz.  of  blasting 
powder  fired  from  a  stemmed  cannon  in  a  7  feet  6  inches  dia- 


Substances  which  form  Explosive  Mixtures.      1 4 1 

meter  gallery,  when  the  atmosphere  contained  no  combust- 
ible gas. 

The  following  requirements  of  the  Coal  Mines  Act  are 
very  important : — 

In  every  mine,  unless  the  floor,  roof,  and  sides  are  naturally 
wet,  arrangements  must  be  made  to  prevent  as  far  as  practic- 
able, coal  dust  from  the  screens  entering  the  downcast  shaft. 

Tubs  shall  be  so  constructed  and  maintained  so  as  to  pre- 
vent coal  dust  escaping  through  the  sides,  ends,  or  floor  of  the 
tub. 

The  floor,  roof,  and  sides  of  the  roads  shall  be  systemati- 
cally cleared  so  as  to  prevent  coal  dust  accumulating. 

Such  systematic  steps  either  by  way  of  watering  or  other- 
wise, as  may  be  laid  down  by  the  regulations  of  the  mine, 
shall  be  taken  to  prevent  explosions  of  coal  dust  occurring 
or  being  carried  along  the  roads. 


QUESTIONS. 

1.  What  would  be  the  effect  of  dropping  a  lighted  match  through 
a  small  hole  into  the  "  gasometer  "  of  a  town  ? 

2.  Steam  is  issuing   in  large  quantities  out  of  a  large  waste  pipe 
and  mixes  with  air.        What  would   be  the  effect   of  introducing  a 
light  into  the  mixture  ? 

3.  A  room  is  believed  to  be  full  of  air  and  gas,  due  to  a  gas  escape. 
Which  will  be  the  safer  way  to  go  into  it :  (i)  using  a  lighted  candle ; 
(2)  using  a  safety  lamp  ? 

4.  Pick  out  from  the  following  mixtures  of  gases  those  which  are 
explosive : — 

Carbon  monoxide  and  air.  Carbon  dioxide  and  coal  gas. 

Carbon  dioxide  and  air.  Bunsen  gas  and  air. 

Methane  and  nitrogen.  Methane  and  air. 

5.  Give  a  sketch  of  any  apparatus  you  know  which  burns  coal  gas 
and  air.     Which   part  of  the  air  and  coal  gas  is  left   unburnt  when 
there  is  a  flame  ?     Do  you  think  the  incombustible  part  helps  to  damp 
down  explosive  effects  ? 

6.  What  would  be  the  effect  of  lowering  a  lighted  lamp  into  a 
chimney  when  in  use  ?     Give  reasons  for  your  answer. 

7.  A   flash  of  lightning  cuts   through  the  air  and  forces  it  apart, 
then   the   two   parts   bang  against   each   other,    producing   thunder. 
Would  you  call  this  an  explosion  ?     Does  it  resemble  one  in  any  way  ? 

8.  Do  you  think  it  is  safe  to  take  the  following  liquids  down  a  mine  : 
Petrol,  ether,  petroleum  ?     Are  any  used  down  the  pit  ? 

9.  What  precautions  are  observed  in  storing,  at  the  pit-head,  lamp 


142  An  Introduction  to  Mining  Science. 

oil  ?  Do  you  think  it  does,  or  does  not  matter,  if  oil  is  carelessly  left 
on  the  outside  of  your  lamp  when  you  take  it  down  the  mine  ? 

10.  What  dangers  are  there  from  smoking  in  the  pit  ?  Supposing 
a  tobacco  could  be  made  which  would  smoke  at  the  same  temperature 
as  your  body,  would  it  be  dangerous  to  smoke  it  in  the  mine  ? 

IT.  What  might  happen  to  a  mixture  of  explosive  gases  from  a  spark 
caused  by  (i)  a  pick  striking  a  piece  of  coal;  (2)  a  nail  in  your  boot 
kicking  a  tram  rail  ? 


CHAPTER  VIII. 
FLAMES:  THEIR  SHAPES  AND  PARTS. 

IT  is  part  of  the  experience  of  most  of  us  to  have  heard  gas 
rushing  out  of  a  gas  jet;  although  invisible  to  us  gas 
always  betrays  its  existence  by  its  smell.  Nevertheless 
when  the  gas  is  lighted  the  smell  disappears  and  in  burning 
gas  becomes  a  very  visible  thing. 

The  two  very  distinct  yellow  and  blue  parts  of  the  flame 
denote  other  changes  going  on  in  the  gas  as  it  burns.  A 
gas  flame  has  a  well-defined  shape,  but  there  is  no  doubt 
that  unburnt  gas  escaping  through  the  same  jet  will  not 
have  the  same  shape,  the  shape  of  the  flame  is  therefore 
influenced  by  its  burning.  The  rush  of  gas  through  a 
burner  of  any  type  influences  the  shape  of  the  flame ;  we 
know  very  well  that  the  tap  has  often  to  be  used  as  its 
regulator.  A  flaring  flame  has  too  much  gas  passing  and 
the  top  of  the  flame  will  smoke  ;  it  has  cooled  down  too 
much  for  thorough  combustion. 

Experiment, 

Turn  on  a  gas  jet,  or  burner  of  any  type,  and  try  to  light  the 
issuing  gas  by  carefully  moving  up,  or  down,  towards  the  source 
of  gas  a  lighted  match  or  candle.  The  issuing  gas  might  be 
explored  all  round  in  this  way,  turning  it  out  at  each  ignition,  to 
find  places  where  it  ignites.  It  will  be  very  evident  if  the  places 
are  noted  that  escaping  unburnt  gas  has  a  very  different  shape 
from  that  of  the  flame. 

The  oil  lamp  flame  of  the  miner  bears  a  great  resem- 
blance to  the  flame  produced  by  the  ordinary  gas  jets,  and 
therefore  a  study  of  these  flames  will  be  interesting. 

143 


144          An  Introduction  to  Mining  Science. 
Experiment, 

Examine   the   gas   pendants   in   the   room  for  gas  burners 
producing  bat's- wing  or  fish-tail  flames.     If  there  are  no  such 


Fish-tail  burner.  Bat's-wing  burner. 

FIG.  73. 

burners  on  the  pendants  obtain  one  and  fix  it  in  the  Bunsen 
tube,  light  it,  and  notice  the  various  parts  of  the  flame.  Make 
diagrams  showing  their  parts  in  your  notebook  (see  Fig.  73). 

The  slit,  or  bat's-wing,  burner  produces  a  flame  in  much 
the  same  manner  as  the  wick  of  the  miner's  lamp,  where 
the  wick  occupies  the  slit  and  brings  up  the  oil  supply. 
In  the  fish-tail  burner  the  gas  issues  as  two  small  streams  at 
right  angles  and  striking  each  other  they  spread  out  flat. 

All  flat  flames  have  an  advantage  over  circular  ones ;  they 
have  a  big  area  from  which  to  pick  up  the  air  necessary  for 
good  light  and  complete  combustion. 

The  illuminating  power  of  a  good  flat  flame  burner  is 
equal  to  that  of  sixteen  candles,  and  so  would  be  described 
as  of  i6-candle  power.  Compare  the  expression  with  that 
used  for  an  engine,  e.g.  an  engine  of  1 6-horse  power,  which 
means  it  can  do  as  much  work  in  a  given  time  as  sixteen 
horses. 

Experiment. 

Move  either  the  head  or  the  stale  end  of  a  match  towards  the 
flame  and  notice  if  there  is  a  non-luminous  outer  envelope  sur- 
rounding the  flame.  A  bit  of  glass  tube  or  rod  shows  the  en- 
velope by  its  becoming  golden  yellow.  Notice  in  the  case  of  a 
lighted  candle  the  position  of  the  free  end  of  the  wick,  and  what 
happens  to  it. 

Before  the  match  gets  to  the  yellow  part  of  the  flame  it 
will  come  into  contact  with  an  almost  invisible  coat  of  highly 


Flames :  their  Shapes  and  Parts.  145 

heated  gas  and  the  head  will  ignite  or  the  stale  blacken.  It 
is  important  to  notice  that  this  happens  before  the  match  has 
reached  the  yellow  part  of  the  flame.  This  outer  invisible 
coat  is  spoken  of  as  the  mantle ;  by  either  word  an  outer 
covering  is  meant.  The  burning  away  of  the  end  of  the  wick 
takes  place  in  the  mantle  of  the  wax  candle ;  it  is  completely 
changed  into  invisible  gaseous  substances  which  pass  into  the 
air.  Compare  the  combustion  of  the  wick  of  the  old- fashioned 
tallow  candle ;  it  chars  and  remains  in  the  middle  of  the 
flame,  never  getting  into  the  mantle ;  its  unburnt  black  mass 
has  to  be  snuffed  or  cut  at  times. 

Experiment, 

Place  a  cool  glass  rod  across  the  flame  of  a  lamp,  candle,  or 
burner,  and  in  the  luminous  part  of  it  notice  the  deposition  of 
soot.  As  the  glass  rod  or  tube  approaches  the  flame  allow  it  to 
stay  in  the  mantle  fora  short  time.  The  yellow  coloration  shows 
the  mantle  very  conspicuously,  but  there  is  no  black  deposit. 

The  experiment  shows  that  there  is  an  inner  portion  of  the 
flame  that  is  shielded  from  the  air  by  the  mantle ;  this  inner 
portion  consists  of  soot  or  carbon,  which  being  shielded  from 
the  air  does  not  immediately  get  burnt,  but  by  the  heat  of 
the  flame  it  gets  yellow-hot  and  so  gives  the  flame  its  lum- 
inosity. 

This  black  substance,  technically  carbon,  and  which  is 
momentarily  formed  in  all  yellow  flames,  must  come  from 
the  substances  burning,  be  it  gas,  oil,  tallow,  wax,  or  coal. 
Beyond  these  substances  carbon  is  found  in  all  animal  and 
vegetable  products ;  all  in  burning  show  yellow  in  their 
flames.  What  becomes  of  the  carbon  in  the  flame  ?  It  gets 
burnt  in  the  mantle  by  the  help  of  the  air,  to  an  invisible 
gas  called  carbon  dioxide. 

It  must  be  remembered  that  the  material  of  the  flame  of 
one  minute  is  not  the  material  of  the  next  minute.  There 
is  a  stream  of  gas  particles  passing  through  the  pipe  and  they 
appear  at  the  gas  jet  to  be  changed  "in  a  moment,  in  the 
twinkling  of  an  eye,''  first  into  visible,  yellow-hot  carbon, 
and  then  into  invisible  carbon  dioxide,  and  their  places  are 
taken  by  others. 

10 


146  An  Introduction  to  Mining  Science. 

Compare  it  with  a  stream  of  smoke  particles  passing  up 
a  chimney  which  gives  a  constant  cloud  of  smoke  at  the  pot. 
A  smoke  banner  and  a  flame  are  different  from  a  flag  float- 
ing from  a  mast ;  the  former  are  composed  of  different 
particles  every  moment  of  their  existences,  the  flag  does  not 
change  its  particles. 

How  Invisible  Gas  becomes  Visible  Flame. 

The  yellow  part  of  the  flame  is  that  part  which  gives 
light  and  is  therefore  of  importance  in  mining,  just  as  it  is  as 
a  scource  of  lighting  in  our  homes.  The  same  yellow  part 
has  to  be  got  rid  off  when  testing  for  fire-damp. 

It  is  plain  that  for  this  yellow  part  to  be  produced 
changes  must  take  place  in  the  gas.  Heat  is  being  pro- 
duced by  the  burning  gas,  for  the  slight  heat  of  the  match 
which  turned  the  gas  into  a  flame  cannot  be,  and  is  not,  re- 
sponsible for  the  large  amount  of  heat  the  flame  produces. 

The  action  of  the  match  on  the  issuing  gas  of  a  burner 
is  very  much  like  setting  fire  to  a  train  of  gunpowder  by 
igniting  one  end ;  if  we  had  a  very  long  train  we  should  have  a 
flare  lasting  for  a  long  time.  In  either  case,  gas  or  powder, 
a  very  fierce  action  starts  between  oxygen  particles  and  the 
particles  of  the  lighted  body.  This  leads  in  the  case  of  the 
flame  to  the  splitting  up  of  invisible  compound  particles 
of  the  gas,  and  black  particles  of  carbon  are  liberated  which 
become  yellow-hot  by  the  heat  of  the  flame ;  thus  the  flame 
gets  a  yellow  part. 

Experience, 

Most  people  have  in  making  toast  burnt  the  bread,  and 
occasionally  may  have  gone  so  far  as  to  set  it  on  fire. 

This  action  is  very  similar  to  that  of  the  heat  of  the  flame 
on  the  original  invisible  gas.  Bread  with  its  white  surface  is 
put  before  the  fire  and  its  heat  splits  up  the  bread  particles, 
liberating  black  particles  of  carbon ;  these  may  even  burn, 
as  in  the  gas  flame,  and  finally  become  carbon  dioxide.  In 
either  case,  then,  no  carbon  particles  are  visible  at  first; 
bread  is  white  and  coal  gas  is  invisible,  but  heat  breaks  up 
their  particles  and  so  reveals  the  unseen  and  hidden  carbon 


Flames :  their  Shapes  and  Parts.  147 

particles.  Such  actions  seem  mysterious,  but  freeing  particles 
from  the  grasp  of  other  particles  reveals  them  all  in  their 
true  properties.  It  is  important  to  remember  that  all  the 
yellow-hot  particles  have  passed  through  the  blue  part  of 
the  flame.  The  size  of  the  blue  part  may  vary  in  a  gas 
flame  according  to  the  quality  of  the  gas ;  a  good  quality 
gas  has  a  large  amount  of  yellow  in  the  flame. 

Experiment, 

Place  a  glass  rod  through  the  blue  part  of  the  flame  ;  no 
soot  will  be  deposited  on  it. 

The  fact  that  one  part  is  visibly  blue  again  shows  that 
changes  have  gone  on  in  the  original  invisible  gas ;  in  the 
blue  part  action  between  air  and  gas  is  very  fierce  and 
there  is  no  chance  for  black  particles  to  exist  in  it  for  even 
a  second  of  time. 

The  blue  part  is  what  might  be  called  the  foundation  of 
the  flame,  for  it  forms  the  base  upon  which  stands  the 
yellow  part. 

Where  there  is  plenty  of  air  mixing  with  gas  there  is  no 
soot  but  much  heat  and  a  blue  flame  are  produced.  The 
same  holds  in  the  case  of  a  gas  stove ;  anything  placed 
thereon  is  not  blackened. 

The  yellow  and  blue  parts  are  very  easily  seen  and  are 
therefore  often  regarded  as  forming  the  complete  flame  ;  we 
know  this  is  not  exact.  There  is  that  almost  invisible  part, 
the  mantle  which  surrounds  the  flame,  rendered  difficult  to 
see  by  the  glare  of  the  yellow  part.  Stars  which  shine  in  the 
daytime  cannot  be  seen  owing  to  the  glare  of  the  sun,  and 
the  "cap"  on  a  miner's  flame  cannot  be  seen  until  the 
flame  is  turned  down  low,  i.e.  the  yellow  or  dazzling  part 
nearly  cut  out.  This  explains  why  it  is  not  easy  to  see  the 
mantle. 

Experiment 

Take  an  ordinary  oil  lamp  with  a  flat  wick,  or  a  gas  pendant 
with  a  flat  flame  burner,  light  and  then  turn  down  the  light 
until  there  is  only  a  blue  band  of  flame  seen.  It  will  only  be 
a  very  small  flame  in  either  case. 

10* 


148  An  Introduction  to  Mining  Science. 


This  flame  is  the  simplest  we  can  get,  its  simplicity  lies 
not  only  in  its  being  of  one  colour  but  also  in  its  being  a 
uniform  mixture  of  air  and  gas,  or  air  and  oil  vapour.  The 
air  in  the  mixture  is  sufficient  to  burn  the  gas  or  vapour 
completely. 

The  full  flame  of  a  miner's  lamp  should  be  well  known 
to  you;  if  it  is  not,  then  light  a  lamp  and  check  off  the 
following  statements : — 

Experiment. 

The  part  of  the  flame  next  to  the  wick  is  a  band  of  pale  blue 
light ;  air  and  oil  vapour  are  here  well  mixed. 

The  next  part  of  the  flame  above  the  wick  is  less  blue  than  the 
above,  it  consists  chiefly  of  unburnt  vapour.  After  the  foregoing 
foundation  of  the  flame  there  is  the  very  visible  luminous  area, 
wh^re  the  carbon  of  the  oil  is  separated  and  becomes  incandes- 
cent. Then  surrounding  the  whole  of  the  flame  is  the  almost 
invisible  mantle. 

Having  fully  made  out  the  foregoing  parts  it  will  be  inter- 
esting to  lower  the  wick  and  by  so  doing  remove  all  the 
yellow  from  the  flame. 

Experiment. 

Notice  the  difference  between  the  position  of  the  wick  in  the 
full  luminous  flame  and  its  position  when  all  the  yellow  is  cut  off. 
In  the  latter  position  there  will  be  seen  in  the  flame  a  dark  band 
in  contact  with  the  metal  tube  of  the  wick  and  a  blue  band 
superposed  on  this  dark  band. 

The  dark  band  consists  of  unburnt  vapour  passing  from 
the  wick  to  the  blue  band  where  it  undergoes  combustion, 
and  the  blue  band  being  well  mixed  with  air  shows  no 
luminosity. 

Experiment. 

Take  a  candle  flame,  or  a  small  gas  flame,  or  a  lamp  flame, 
and  using  a  mouth  blowpipe  blow  air  gently  into  the  flame  ;  the 
luminosity  will  disappear. 

This  method  of  mixing  air  and  gas  or  vapour  results  in  a 
loss  of  light  but  in  an  increase  of  heating  power ;  it  has  practi- 
cal applications  for  lighting  as  well  as  for  heating  purposes. 


Flames:  their  Shapes  and  Parts.  149 

It  is  therefore  very  plain  that  if  a  sufficient  quantity  of 
air  could  be  mixed  with  coal  gas  the  yellow  part  of  the  flame 
would  not  be  formed,  and  a  vessel  being  heated  would  not 
be  blackened  by  the  soot  or  carbon. 

The  foregoing  part  of  this  book  has  in  many  ways  brought 
us  into  contact  with  the  necessity  of  air  in  combustion,  and 
incidentally  it  has  been  seen  that  where  the  parts  of  a  flame 
are  colourless  there  is  plenty  of  air  present.  If  air  is  mixed 
with  gas  in  certain  quantities,  on  burning  the  mixture  the 
flame  is  colourless. 

Experience, 

The  incandescent  gas  burner,  which  is  now  known  to  every  one, 
has  four  holes  through  which  air  passes  and  then  mixes  with  gas 
which  burns  with  a  non-luminous  flame,  in  this  the  mantle  is 
supported.  Gas  stoves  used  for  cooking  purposes,  or  the  heating 
of  rooms,  have  air  inlets,  and  after  passing  in  the  air  mixes  with 
the  gas,  a  non-luminous  flame  being  produced. 

The  burner  called  the  Bunsen  burner,  used  as  a  source  of 
heat  in  science  work,  is  historically  and  industrially  of  im- 
portance because  it  has  given  rise  to  all  burners  which  mix 
air  with  gas.  Prof.  Bunsen  of  Heidelberg  required  a  burner 
which  would  not  blacken  his  vessels  when  being  heated,  and 
from  this  necessity  and  his  scientific  knowledge  he  devised 
the  burner  we  use ;  it  is  shown  in  Fig.  74,  p.  150. 

Experiment. 

Take  a  Bunsen  burner  and  screw  off  the  gas  tube  and  then 
notice  the  gas  nipple  on  the  base  of  the  burner ;  it  is  connected 
with  the  gas  supply  pipe.  See  that  the  ring  or  collar  on  the  tube 
is  capable  of  being  turned  so  as  to  close  or  open  the  two  air-holes. 

The  air  flows  in  at  the  air-holes,  or  intake,  as  the  coal  gas 
rushes  out  of  the  fine  gas  jet ;  this  uprush  of  gas  is  the 
cause  of  the  flow  at  the  air-holes;  thus  the  outside  air 
continues  to  pass  into  the  tube  through  the  "air  intakes," 
one  of  which  is  shown  in  Fig.  74. 

The  air  that  is  passed  in  mixes  with  the  uprushing  gas  and 
all  the  carbon  particles  are  burnt  to  carbon  dioxide  before 
they  can  appear  as  luminous  particles  which  blacken  a  body 
when  heated  in  a  purely  coal-gas  flame. 


150          An  Introduction  to  Mining  Science. 


FIG.  74.  —  The  Bunsen 
burner,  showing  an  air- 
hole. 


The  mixture  of  air  and  gas  burns  at  the  top  of  the  tube  ; 
this  is  because  the  mixture  flows  out 
more  quickly  than  the  flame  can 
travel  down. 

The  size  of  the  air  inlet  may  be 
regulated  by  a  sliding  ring,  which  is 
usually  when  in  use  turned  until  the 
flame  is  entirely  blue  and  burns 
quietly. 

The  Bunsen  burner  should  not 
have  its  nipple  burning  when  a  flame 
is  at  the  top  of  the  tube,  if  this  be 
the  case  there  will  be  a  disagreeable 
odour  and  soot  will  be  deposited  on 
any  object  being  heated. 

A  practical  application  of  the 
Bunsen  burner,  just  as  Bunsen  con- 
structed it  for  his  laboratory  except 
as  regards  size,  is  found  in  the  heat- 
ing of  coke  ovens.  The  following 
measurements  and  figures  obtained  from  a  Yorkshire 
colliery  working  coke  ovens  will  be  interesting  : — 

Length  of  burner         .        .  42  in. 

Diameter        .        .       .        .  if  in. 

Air  intake      .        .        .       .  if  in.  long,  f  in.  wide. 

Collar  for  regulating  intake  2|  in.  depth,  if  in.  diameter. 

Diameter  of  gas  nipple       .  J  in. 

Compare  these  figures  with  measurements  of  the  Bunsen 
burner  used  in  your  scientific  work. 

There  are  fifteen  burners  to  each  coke  oven,  fixed  directly 
to  the  main  pipe,  and  each  one  consumes  nearly  140  cubic 
feet  of  gas  per  hour.  It  is  necessary  to  get  the  highest  tem- 
perature, hence  mixed  with  this  140  cubic  feet  are  700 
cubic  feet  of  air,  so  that  gas  is  to  air  in  the  ratio  of  one  to 
five.  It  is  worth  mentioning  that  the  chambers  under  the 
coke  ovens  where  these  Bunsen  burners  are  fixed  have  a 
temperature  of  90°  to  100°  C.,  a  temperature  that  bites 
your  ears  and  nose  as  you  pass  through  the  chambers. 


Flames  :  their  Shapes  and  Parts.  I  5 * 

That  the  air  is  the  active  substance  in  rendering  the  coal 
gas  non- luminous  and  therefore  giving  us  the  Bunsen  flame 
may  easily  be  shown. 

Experiment, 

Close  the  air  intake  of  the  Bunsen  and  a  luminous  flame  is 
obtained,  then  gradually  introduce  air  by  opening  the  holes 
again  and  notice  the  whole  flame  becomes  mantle-like.  Test 
for  any  soot  in  the  flame.  Show  the  presence  of  an  air  current 
at  the  holes  by  holding  a  piece  of  smouldering  paper ;  the 
smoke  is  drawn  into  the  tube. 

The  air  completely  destroys  the  luminosity  of  the  flame. 

It  will  be  interesting  to  know  the  amounts  of  air  and 
coal  gas  which  pass  up  the  Bunsen  tube ;  they  are  generally 
about  2  cubic  feet  of  air  to  i  cubic  foot  of  gas,  but 
vary  slightly  with  different  burners.  The  following  figures 
show  the  variation  : — 

Air     63  per  cent.  Air     7 1  per  cent. 

Gas     37         „  Gas    29       „ 

100  100 

Compare  these  figures  with  those  for  the  industrial 
Bunsen  burner. 

Experiment, 

Hold  for  a  minute  or  two  an  inverted  gas  cylinder  over  a 
Bunsen  burner  when  unlit  gas  is  issuing  ;  the  air  will  be  displaced. 
Apply  a  light  to  the  mixture  and  note  its  burning  with  a  non- 
luminous  flame,  also  its  sudden  combustion  throughout  the 
cylinder. 

It  is  worth  noticing  that  although  the  time  which  elapses 
between  the  air  finding  its  way  in  at  the  air  intake  holes 
and  issuing  at  the  top  with  the  gas  is  very  short,  the  two 
have  nevertheless  become  uniformly  mixed. 

The  Structure  of  a  Bunsen  Flame. 

When  the  Bunsen  flame  is  burning  in  a  satisfactory 
manner  it  will  be  seen  to  have  two  very  distinct  parts  :  an 
inner  part  and  an  outer  bluish  part. 


152          An  Introduction i  to  Mining  Science. 


Experiment. 

Light  a  Bunsen  burner  and  then  slowly  bring  down  on  to  the 

flame  a  piece  of  wire  gauze,  as 
shown  in  Fig.  75.  After  hold- 
ing it  in  this  position  for  a  few 
seconds  a  red-hot  ring  will  be 
seen.  What  does  this  experi- 
ment prove  ? 

There  cannot  be  flame  in 
the  middle,  or  the  cold  inner 
circle  could  not  exist. 

The  gas  which   comes   up 
the  tube  burns  fiercely  where 
it  comes  into  contact  with  the 
air,   but   this   fiercely  burning 
outside  protects  the  inside  gas 
from  the  air  and  so  its  combus- 
tion is  momentarily  prevented. 
We  may  therefore  say  that  the  gas  at  the  top  of  the  tube 
forms  an  inner  cool  part  and  an  outer  hot  part,  which  is  the 
real  flame  and  mantle-like  in  appearance. 

Depress,  and  remove  quickly  when  charring    commences,  a 
piece  of  white  paper  on  a  Bunsen  flame  and  notice  the  concentric 


FIG.  75. — Showing  the  red-hot 
ring. 


FIG.  76. — Showing  the  charred  paper ;  a  ring  or  ellipse  is  formed 
according  to  position. 

circles  formed.     Get  in  the  same  manner,  half-way  up,  a  trans- 
verse section  of  the  luminous  flame. 


Flames :  their  Shapes  and  Parts. 


153 


The  paper  shows  a  charred  ring  with  an  inner  circle  of  un- 
touched paper.  It  is  plain  that  we  are  dealing  with  an  inside 
hollow  cylinder  of  cool  gas  surrounded  by  a  highly  heated 
flame. 

Further  Experiments  on  the  Bunsen  Flame, 

Introduce  horizontally,  and  quickly,  a  match  into  the  middle 
of  the  flame.  Or  fix  a  match  in  the  tube  by  a  pin  penetrating 
the  match  at  right  angles  and  then  light  the  Bunsen  (see  Fig.  77). 

Lead  out  from  the  inner  cone  unburnt  gas  by  a  small  tube 
held  in  this  part  and  at  an  angle  of  70°  (see  Fig.  78). 

It  is  plain  that  the  temperature  of  the  mixed  gas  and 
air  which  feeds  the  Bunsen  flame  is  lower  than  that  required 


fl75°C 


I533°C--- 

/333°C--- 
I75°C-- 


A 

A 

C 


/O9O  C 


--   54  °C 


FIG.  77. 


FIG.  78. 


FIG.  79. — Diagram  showing  tem- 
peratures of  different  parts  of 
the  Bunsen  flame. 


to  ignite  the  match  ;  it  even  fails  to  get  warmed  enough  for 
ignition  to  occur  if  left  a  long  time  in  its  position. 

The  Bunsen  flame  is  therefore  hollow,  which  means  that 
it  does  not  consist  entirely  of  burning  gas.     If  flame  is  de- 


154          An  Introduction  to  Mining  Science. 

fined  to  be  gas  in  a  burning  state  then  the  word  does  not 
include  the  inner  cone  of  unburnt  gas;  the  word  flame  in 
ordinary  life  means  the  whole  structure  at  the  gas  exit  tube. 
It  will  be  instructive  to  point  out  that  the  temperature  at 
different  parts  of  a  flame  varies ;  the  luminous  and  non- 
luminous  flames  of  the  Bunsen  burner  may  be  taken  as  ex- 
amples. 

Distance  up  flame.  Luminous  Bunsen 

flame.  flame. 

•J  inch  above  burner        .          .  135°  C.  54°  C. 

ii  >,             »                 •  42I°  C.  175°  C. 

Tip  of  inner  cone,  C.         .         .  913°  C.  1090°  C. 

Centre  of  outer  cone        .         .  1328°  C.  !533°  C. 

Tip  of  outer  cone  .          .          .  728°  C.  1175°  C. 

Outer  cone  level  with  inner  tip  1236°  C.  I333°  C. 

It  should  be  noticed  that  the  first  effect  of  the  air  (see 
the  first  two  figures  in  the  second  and  third  columns)  is  to 
cool  the  flame,  but  after  these  are  passed  the  temperature  is 
higher  in  the  Bunsen  flame  than  in  the  corresponding  lumin- 
ous parts.  The  average  temperature  of  the  Bunsen  flame 
is  in  round  numbers  894°  C,  and  that  of  the  luminous  flame 
760°  C. 

The  position  of  the  highest  temperature  is  worth  noticing, 
about  two- thirds  up  the  flame  (see  Fig.  79). 

The  Bunsen  flame  may  be  regarded  as  made  up  of  two 
cones — a  cone  of  gas,  C  ;  a  cone  of  flame,  A.  There  is, 
where  the  cone  A  fits  on  C,  a  small  area  of  a  distinct  colour 
but  of  no  importance.  In  the  cone  A  there  is  complete 
combustion  of  the  gas  but  in  the  cone  C  there  is  no  com- 
bustion. Where  these  two  cones  meet  there  is  fierce 
combustion,  the  area  of  it  is  small  but  very  distinct  by  its 
greenish  colour. 

Flame — burning  gas — has  now  been  considered  along 
with  devices  for  increasing  and  decreasing  its  luminosity, 
depending  on  whether  the  flame  is  to  be  used  for  lighting 
or  heating  purposes. 

The  great  change  brought  about  in  coal  gas  by  its  burning 
is  made  plain  in  the  following  table  and  statement. 


Flames :  their  Shapes  and  Parts. 


155 


Composition  of  unburnt  coal  gas  : — 

-  Hydrogen  ..... 
Marsh  gas  .... 

Carbon  monoxide       .          .          . 
Nitrogen    . 

Ethylene    ..... 
Carbon  dioxide  . 


51-4  per  cent. 

34'3 
7'4 

2-2 

4'4 

'3 


lOO'O 


The  components  of  burnt  coal  gas  will  be  far  simpler ; 
there  will  only  be  three,  viz.  nitrogen,  carbon  dioxide,  and 
water  vapour.  The  water  vapour  condenses  to  water  as 
soon  as  it  cools. 

Experience  of  Light  without  Flame, 

The  incandescent  electric  lamp,  one  variety  of  which  is  shown 
in  Fig.  80,  is  to  be  seen  in  all  tramcars, 
most  public   halls,   and  many  private 
houses. 

The  lamp  consists  of  a  glass  bulb, 
which  is  quite  devoid  of  air,  with  a 
thin  wire-like  length  of  material  of  about 
12  inches  long  and  less  than  ^  of  an 
inch  thick — called  the  filament ;  it  is  in 
loops,  through  which  the  current  of 
electricity  runs. 

In  public  lighting  a  current  of 
electricity  passes  along  cables,  made 
of  copper,  fixed  below  the  surface  of 
the  street,  but  when  the  current 
comes  to  traverse  the  filament  of 
the  lamp  it  meets  with  great  resist- 
ance, and  having  to  force  its  way 
through,  heat  is  produced ;  this  heat 
makes  the  filament  white-hot  and  so 
it  gives  off  light. 

No  combustion  can  take  place  in  the  lamp  because  there 
is  no  air  inside ;  the  light  is  therefore  derived  from  an  in- 
candescent metallic  filament.  In  the  older  lamps  a  carbon 
filament  was  used. 


FIG.  80. — An  electric 
lamp. 


156  An  Introduction  to  Mining  Science. 

Experience. 

Most  people  are  familiar  with  the  pocket  flash-lamp.  The 
bulb  part  of  the  lamp  contains  a  filament  for  the  current  to 
traverse  ;  it  may  be  seen  by  opening  the  upper  cover.  The  dry 
battery,  or  dry  cell,  which  fills  the  case  has  to  be  renewed  in 
order  to  continue  the  lamp's  light-giving  power.  These  cells 
contain  various  chemicals,  such  as  plaster  of  Paris,  zinc  chloride, 
and  sal  ammoniac,  along  with  zinc  or  carbon  rods. 

The  circuit  or  path  for  the  current  is  completed  by  press- 
ing a  button  ;  chemical  action  at  once  takes  place  in  the  cell, 
and  this  produces  electricity,  which,  passing  through  the 
filament,  is  changed  into  heat  and  light.  Compare  the 
foregoing  with  the  miner's  electric  lamps  described  on  p.  102. 

QUESTIONS. 

1.  Make  a  sketch  of  the  flame  of  a  miner's  lamp  showing  the  three 
parts.     Which  part  of  the  flame  would  blacken  a  body  if  placed  in  it  ? 

2.  Explain  the  difference  in  the  production  of  light  between  an  in- 
candescent burner  and  a  bat's- wing  one. 

3.  Are  there  any  differences  between  a  gas  cap  and  the  mantle  of  a 
flame? 

4.  A  smoky,  dull,  and  irregular  flame  becomes  smokeless,  bright 
and  regular  when  a  glass  chimney  is  fixed  around  it,  or  when  the 
wick  is  turned  down.     Explain  these  changes. 

5.  Describe  with  diagrams  any  methods  of  producing  light  without 
flame.     Are  these  methods  dependent  on  air  for  their  light  ? 

6.  Explain  why  a  coke  fire  will  not  blacken  objects  placed  on  it  for 
heating  or  boiling  purposes. 

7.  Carbon  (soot)  is  often  deposited  in  the  fire-grate  back  or  on  its 
bars  when  a  fire  is  burning.     Observe  all  you  can  in  connexion  with 
the  deposition  and  then  give  the  reasons  for  it. 

8.  Which  do  you  consider  is  the   light-giver  in  an  incandescent 
burner,  the  mantle  or  the  burning  gas  ?     Give  reasons. 

9.  Consider  the  following  three  pairs  of  facts  of  common  experience, 
and  give  an  explanation  of  each  difference : — 

(a)  The  characteristic  smell  of  coal  gas. 

(b)  The  loss  of  smell  on  burning. 

(c)  The  deposition  of  soot  on  articles  by  a  luminous  flame. 

(d)  The  absence  of  deposit  in  a  Bunsen  flame. 

(e)  The  high  temperature  of  the  flame. 

(/)  The  heat  of  the  match  is  all  that  is  initially  supplied. 

10.  Explain  why  a  taper  will   not   burn  in  coal  gas.     Name  the 
gases  into  which  a   taper  has  turned  when  it  has  been  completely 
burnt. 

it.  What  is  a  flame  ?  Methylated  spirit  burning  gives  a  blue 
flame  ;  do  you  think  there  is  any  incandescent  carbon  in  it  ? 


CHAPTER  IX. 
WAYS  OF  PRODUCING  HEAT  AND  LIGHT. 

IN  the  production  of  light  there  is  always  heat  preceding 
its  appearance ;  only  when  the  heat  has  become  fierce  does 
light  begin  to  show  itself. 

In  a  pit  there  is  a  great  deal  of  heat  at  a  low  temperature 
produced  by  the  friction  of  one  thing  on  another,  e.g.  coal 
tubs  running  on  the  rails,  and  there  is  always  some  coal 
being  ground  to  a  very  fine  and  dry  dust.  The  use  of  coal 
cutters  in  the  pit  must  result  in  the  making  of  the  cutting 
part  of  the  machine  very  hot,  and  fine  coal  dust  is  also 
produced.  It  is  worth  emphasizing  that  by  both  these  pro- 
cesses fine  coal  dust  is  produced  as  well  as  heat.  The  in- 
flammability of  dry  coal  dust  is  one  of  the  chief  factors  in 
pit  explosions. 

Experience, 

That  heat  is  produced  by  the  rubbing  of  one  substance  upon 
another  substance,  or  a  piece  of  itself,  is  widely  known.  The 
joiner  finds  his  saw  gets  hot  as  he  cuts  through  a  plank  of  timber, 
and  even  the  sawdust  is  in  a  hot  condition.  Metal  and  wood 
when  scraped  or  planed  also  show  an  increase  of  temperature, 
as  do  the  scrapings  and  shavings. 

If  the  material  scraped,  sawn,  or  planed  off  consisted 
of  a  fine  dry  dust  then  we  feel  certain  that  it  might  more 
easily  catch  fire  by  the  heat  produced,  and  so  burst  into 
flame,  than  if  it  were  coarse  and  moist.  The  production  of 
heat  by  rubbing,  i.e.  friction  of  surfaces  on  one  another,  is 
well  known  to  all  boys  in  the  familiar  prank  of  rubbing  a 
button  on  a  surface  and  then  placing  it  on  a  friend's  cheek. 
The  heating  of  the  hands  on  slipping  down  a  long  length 


158  An  Introduction  to  Mining  Science. 

of  rope  is  also  well  known.     All  movement  of  surfaces  in 
contact  produces  big  or  little  amounts  of  heat. 

As  far  back  as  1875  it  was  shown  that  a  mixture  of  air 
and  fire-damp,  which  could  not  be  ignited  by  a  naked  light, 
showed  a  tendency  to  ignite  when  coal  dust  was  added. 
The  ignition  of  coal  dust  resulting  in  an  explosion  was 
shown  in  the  experiments  at  Altofts  in  1908  and  1909; 
gas  was  entirely  absent  in  one  experiment  when  the  exploding 
mixture  of  coal  dust  and  air  blew  one  piece  of  a  boiler  shell, 
weighing  40  lb.,  a  quarter  of  a  mile. 

In  order  to  emphasize  this  point  of  the  inflammability  of 
dry  dust,  the  following  old  methods  of  producing  fire,  before 
matches  were  invented,  by  primitive  man  are  worth  con- 
sidering. One  which  was  a  world-wide  process  may  be 
illustrated  by  the  following  experiment. 

Experiment, 

Take  a  round  piece  of  wood,  e.g.  a  ruler,  and  rotate  it  between 
the  palms  of  the  hand  by  sliding  the  latter  backwards  and  for- 
wards. Keep  the  lower  end  of  the  ruler  on  a  piece  of  wood. 
Heat  is  produced  where  the  ruler  grinds  on  the  wood.  It  might 
be  detected  by  placing  the  bulb  of  a  thermometer  on  the  place 
rubbed.  The  hands  and  ruler  also  become  warm. 

In  the  primitive  method  dry,  hard  wood  was  used/ and  by 
the  friction  of  the  rotatory  part  hot  wood  dust  was  made. 

Another  process  consisted  of  quickly  drawing  one  piece 
of  wood  in  the  groove  of  another  piece  until  heated  wood 
dust  was  produced.  In  a  similar  process  dry  bamboo  with 
a  saw-like  edge  was  used  on  another  piece  and  the  usual 
hot  dust  produced.  In  all  cases  this  hot  dust  was  arranged 
to  fall  upon  very  dry  grass  or  dried  hairy  seeds  of  plants, 
similar  to  thistle  or  dandelion  so  as  to  ignite  them.  When 
fire  had  been  obtained  in  this  way  a  wood  fire  was  usually 
kept  continually  going,  often  in  a  place  of  worship.  The 
foregoing  facts  should  bring  home  to  us  the  inflammability 
of  combustible  substances  when  in  a  fine  and  dry  condition  ; 
the  finer  and  drier  they  are  the  easier  it  is  to  bring  about 
their  ignition.  It  is  therefore  plain  that  any  source  of  high 
temperature  in  a  pit,  e.g.  the  bonnet  of  too  hot  a  lamp,  is 


Ways  of  Producing  Heat  and  Light.          159 

a  source  of  danger  if  there  be  fine  and  dry  coal  dust  present. 
Those  who  work  in  dry,  hot,  and  dusty  pits  know  that  the 
inflammability  of  coal  dust  is  counteracted  by  stone  dusting 
the  various  parts  of  the  pit ;  it  is  covering  or  mixing  inflam- 
mable dust  by  a  non-combustible  dust. 

The  Development  of  the  Match. 

The  way  in  which  the  human  race  progressed  in  the 
making  of  "  fire  "  should  be  interesting  to  us ;  the  fore- 
going paragraphs  show  the  first  steps  to  be  the  making  of  a 
hot  dust,  the  next  and  the  final  stages  in  the  production  of 
a  match  has  important  lessons  to  the  miner.  As  soon  as 
mankind  knew  how  to  make  steel  they  began  to  change  the 
materials  used  in  making  "fire  ".  Steel  and  flint  came  into 
action ;  flints  are  very  similar  to  the  hard  pebbles  found 
on  the  coast,  sometimes  they  are  used  in  paving  streets. 
In  the  striking  of  flint  and  steel  sparks  were  produced, 
and  these  red  or  white-hot  sparks  fell  on  dry  tinder  so 
arranged  as  to  catch  the  sparks. 

Experience. 

The  production  of  sparks  by  friction  or  grinding  is  a  part  of 
every  one's  experience.  The  brakes  on  the  engine  give  a  torrent 
of  sparks  when  applied  to  moving  wheels  ;  the  shoe  placed  on 
the  wheel  of  a  cart  produces  sparks  as  it  is  dragged  over  the 
stones  of  a  street  or  road.  The  iron  shoe  of  the  horse  and  the 
iron  nails  of  a  man's  boots  are  often  producers  of  sparks  when 
they  come  violently  into  contact  with  the  paving-stones. 

Fig.  8 1  shows  a  machine  for  making  sparks;  the  cog  wheels 
rotate  a  steel  disc  fixed  on  the  same  axis  as  the  small  cog 
wheel.  A  shower  of  sparks  is  obtained  by  pressing  the 
piece  of  flint,  shown  in  the  figure  on  the  supporting  board, 
lightly  against  the  edge  of  the  revolving  steel  disc.  On 
the  right  of  the  figure  is  a  gas  nozzle  through  which  different 
gases  may  issue  so  as  to  experimentally  find  if  the  gas  can 
be  ignited  by  the  sparks.  By  this  particular  machine  hydro- 
gen is  instantly  ignited,  while  the  same  temperature  sparks 
fail  to  ignite  marsh  gas.  Consider  this  in  connexion  with 
the  employment  in  pits  of  coal-cutting  machines  which  have 
increased  very  much  during  the  last  few  years;  the  cutter 


160  An  Introduction  to  Mining  Science. 

of  the  machine  is  a  wheel  or  disc  with  chisels  set  in  its  rim. 
The  rate  at  which  the  disc  revolves,  from  sixty  to  eighty 
revolutions  per  minute,  and  the  resistance  it  has  to  over- 
come in  the  cutting  must  produce  much  heat  and  often 
sparks,  particularly  where  it  cuts  through  "  brassy  "  coal, 
and  this  no  doubt  makes  the  process  not  free  from  danger 
in  a  gassy  pit.  Coal-cutting  machines  electrically  driven 


FIG.  81. — Machine  for  making  sparks. 

may  give  an  electrical  spark  and  so  produce  an  explosion, 
as  was  alleged  in  the  Wharncliffe  Silkstone  explosion  of 
1914. 

The  foregoing  methods  of  producing  a  light  would  all  be 
regarded  as  very  slow  if  they  had  to  be  employed  at  the 
present  day ;  it  is  important  to  notice  that  they  all  consist 
of  making  a  substance  hot  by  friction,  and  the  substances 
used  were  not,  except  tinder,  inflammable  ones.  The  next 
step  in  the  production  of  a  light  consisted  of  making  a 
match,  although  different  from  the  present-day  one.  The 


Ways  of  Producing  Heat  and  Light.         161 

match  as  we  know  it  produces  much  heat  and  light  for  the 
small  amount  of  friction  given  on  the  box  surface :  this  is 
because  the  head  consists  of  substances  easily  ignited,  or  in 
other  words,  of  chemicals  which  are  artificially  made.  The 
match  flares  up  suddenly  by  chemical  action ;  this  flare  is 
produced  after  the  slight  rubbing  which  starts  the  action. 

Many  chemical  methods,  i.e.  methods  involving  the  use 
of  chemicals,  were  invented  between  the  years  1780  and  1840 
of  producing  fire,  or  a  light  as  we  should  now  say,  but  in 
the  latter  year  friction  matches  came  into  existence. 

One  of  the  first  kind  of  matches  made  consisted  of  a  piece 
of  wood  with  a  brimstone  head. 

Experiment, 

Take  a  small  amount  of  sulphur,  i.e.  brimstone,  and  melt  it 
over  a  flame  turned  down  low  ;  it  may  be  melted  on  a  tin  lid  or 
any  bit  of  pot.  When  melted  dip  in  bits  of  wood  so  as  to  put  a 
cap  of  sulphur  on  them. 

These  matches  might  be  used  for  carrying  a  light  from  one 
place  to  another,  the  presence  of  the  sulphur  on  them  helps 
to  make  certain  of  the  wood-stick  taking  fire.  They  were 
at  the  beginning  of  the  nineteenth  century  dipped  into  a 
mixture  of  phosphorus,  oil,  and  wax,  and  then  ignited  by 
rubbing  on  a  cork.  The  phosphorus  ignited  first,  and  then 
set  the  sulphur  on  fire,  and  this  acted  on  the  wood. 

Johann  Jrinyi,  a  Hungarian,  improved  on  the  sulphur- 
tipped  match  by  adding  phosphorus  to  the  sulphur.  He 
learnt  this  from  experiments  made  at  lectures  which  he  at- 
tended. This  produced  the  ordinary  match  which  will 
ignite  on  any  surface  when  it  is  rubbed  sufficiently.  R. 
Bell  commenced  the  manufacture  of  this  match,  called 
a  lucifer  match,  in  London  in  1832  ;  it  was  ignited  by 
drawing  through  sandpaper. 

Experiment, 

Strike  a  match  and  immediately  try  to  blow  out  the  flame. 
Can  you  do  so  before  the  head  has  completely  burnt  ? 

Notice  the  pitted  nature  of  the  head  after  combustion,  and 
that  the  burning  of  the  head  is  not  as  gentle  as  that  of  the 
stick. 

II 


1 62  An  Introduction  to  Mining  Science. 

Stopping  the  combustion  of  the  head  will  not  be  easy 
to  accomplish  ;  if  it  does  occur  it  is  because  your  blowing  has 
cooled  the  head  down  below  the  temperature  required  for 
burning.  Difficulty  in  stopping  the  combustion  is  due  to 
the  fact  that  its  burning  is  independent  of  the  air. 

The  pitted  nature  of  the  head  and  its  vigorous  combustion 
suggest  we  are  dealing  with  a  highly  inflammable  mixture  ; 
in  fact  the  burning  of  the  head  suggests  a  fiery  mixture  akin 
to  an  explosive. 

Experiment, 

Strike  a  match  and  immediately  notice  the  colour  of  the  flame 
of  the  burning  head.  Is  there  a  change  in  the  colour  of  the 
flame  as  it  passes  from  match-head  to  stick  ? 

It  will  be  noticed  that  the  colour  of  the  flame  changes 
as  the  burning  passes  from  the  head  to  the  stick.  The  stick 
burns  with  that  type  of  flame  common  to  oil,  gas,  wax, 
tallow,  and  coal  gas  ;  it  has  a  blue  and  a  yellow  part.  The 
head  is  distinctly  bluish-white  as  it  flares,  and  it  is  uniformly 
of  one  colour ;  a  reference  to  the  Table  of  Colours  on  p.  8 
will  tell  us  it  has  a  very  high  temperature. 

Experience. 

Recall  the  experience  you  have  had  in  connection  with  fire- 
works ;  in  burning  they  give  various  displays  of  colour,  and  burn 
with  great  energy.  The  colour  of  the  flame  of  the  match-head 
may  be  recalled  as  having  been  seen  during  a  firework  display. 

In  match-heads  and  fireworks  the  vigour  of  the  burning 
is  due  to  their  containing  chemicals  rich  in  oxygen  ;  the 
chemicals  which  burn  do  not  have  to  get  their  oxygen  from 
the  air,  it  is  part  and  parcel  of  the  substances  mixed  in  the 
head.  The  colour  of  the  flame  shows  the  head  contains 
nitrate  of  potash,  or  chlorate  of  potash ;  it  is  the  potash 
which  gives  the  bluish- white  or  lilac- coloured  flame  of  the 
burning  head. 

Why  should  any  consideration  be  given  to  the  making 
and  burning  of  a  match  ?  Well,  it  brings  us  into  contact 
with  two  sources  from  which  a  burning  substance  may  get 
its  oxygen  ;  one  source  is  from  the  air  and  the  other  from 


Ways  of  Producing  Heat  and  Light.         163 

the  burning  substance  itself.  The  latter  is  always  the  case 
with  fiercely  and  rapidly  burning  substances  such  as  ex- 
plosives and  fireworks.  A  match  and  its  changes  on  com- 
bustion afford  an  excellent  lesson  in  chemistry,  and  so  merit 
our  consideration  on  account  of  their  familiarity. 

Experiment, 

Try  if  a  match-head  will  burn  in  carbon  dioxide.  This  may 
be  done  by  putting  an  unstruck  match  in 
a  jar  of  the  gas  and  touching  the  head 
with  a  hot  rod.  Or  strike  the  match  in 
the  jar  and  see  if  the  match  will  burn 
beyond  the  head  part. 

The  apparatus  shown  in  Fig.  82  may 
be  used  for  the  purpose,  the  unstruck 
match  being  fastened  on  a  piece  of  wire 
and  then  touched  by  a  hot  rod  of  any 
kind  of  material. 

The  condition  of  a  match  in  the 
burnt  and  unburnt  states  brings  us 
face  to  face  with  a  great  change,  such 
a  change  that  it  might  be  regarded 

as  a  great  transformation  if  it  were  FlG-  8?-"rBjr"mgJ  a 
i  r  •!•  T>  c.  a-u  i  match-head  fixed  on 

less  familiar  to  us.     By  fire  the  clean,         to  wire>  in  a  cyiinder 

smart-looking  match  is  transformed  containing  carbon 
into  a  useless  substance  which  soils  dioxide, 
the  fingers.  The  change  is  called  a  chemical  change,  because 
there  are  great  differences  between  the  substances  forming 
the  match  before  and  after  igniting  it.  The  change  of  colour, 
the  production  of  a  smell,  the  outburst  of  flame,  the  perman- 
ent alteration  in  appearance  all  indicate  a  chemical  change. 
The  ease  with  which  a  match  will  ignite  tells  us  that 
some  solid  substances  are  easily  inflammable ;  the  rubbing, 
or  friction,  of  the  match  on  the  box  surface  cannot  produce 
much  heat,  but  there  is  sufficient  to  set  the  head  ablaze. 

The  Chemical  Teaching  of  a  Match, 

In   the   experiment   on   removing    oxygen    from   air   by 
using  phosphorus  a  hot  rod  was   used  to  bring  about  its 

II  * 


164          An  Introduction  to  Mining  Science, 

ignition.  Phosphorus,  which  goes  by  the  name  of  yellow, 
or  white,  phosphorus,  has  to  be  used  with  care,  otherwise 
it  quietly  bursts  into  flame.  It  was  used  in  match-making 
up  to  the  end  of  the  year  1909,  but  then  forbidden  by 
law  because  it  is  poisonous.  If  yellow  phosphorus  is  heated 
in  carbon  dioxide  gas  it  changes  to  a  red  colour  and  be- 
comes far  less  active  and  vigorous.  It  is  a  curious  result, 
for  this  red  phosphorus  remains  unaltered  in  the  air,  is  not 
as  easily  ignited  as  yellow  phosphorus,  and  is  not  poisonous. 
Red  phosphorus  is  now  used  in  match-making. 

Experiment. 

Rub  a  safety  match  gently  on  the  striking  surface  of  the  box 
in  a  dark  place  and  see  if  any  light  is  produced.  A  bright  line 
may  be  seen  as  the  match  passes  along  the  surface,  the  heat 
may  ignite  the  match-head.  Set  fire  to  the  striking  surface  and 
establish  the  presence  of  phosphorus  in  it  by  smell  and  combus- 
tion. 

The  striking  surface  should  be  set  on  fire  by  a  Bunsen 
flame,  and  if  there  be  phosphorus  in  it  a  wave  of  combustion 
will  be  seen  to  slowly  travel  over  the  surface,  and  white 
fumes,  which  possess  an  unpleasant  garlic-like  smell,  will 
be  perceived. 

The  bright  line  seen  in  the  experiment  is  due  to  the 
heat,  produced  by  the  friction,  turning  the  red  phosphorus 
in  the  striking  surface  back  again  to  yellow  which  immedi- 
ately inflames. 

If  the  foregoing  experiment  is  done  in  the  dark  it 
will  then  be  seen  in  the  case  of  safety  matches  that  the 
phosphorus  on  the  box  is  first  ignited  and  after  this  the 
head. 

Experiment, 

By  burning  matches  prove  the  production  of  the  following 
substances  during  combustion  :  Carbon,  ash,  carbon  dioxide. 

Some  carbon  has  burnt  away  as  carbon  dioxide  ;  this  is  easily 
proved  by  burning  the  match  in  a  bottle  or  gas  jar  (see  Fig.  82, 
p.  163).  The  vessel  may  be  held  over  the  burning  match  ;  in  any 
case  the  carbon  dioxide  is  detected  in  the  vessel  by  shaking  with 
lime  water. 


Ways  of  Producing  Heat  and  Light.         165 

A  match  after  burning  usually  shows  three  parts :  an  un- 
burnt  part ;  the  part  held  in  the  fingers,  nearer  the  head  a 
black  part ;  and  at  the  head  end  a  frail  fluffy  part  of  a  grey 
or  white  colour. 

This  latter  part  is  the  ash,  and  is  incombustible  material. 
In  the  ash  part  of  the  burnt  match  the  carbon,  liberated 
from  the  wood  of  the  stale  as  the  match  burnt,  has  burnt 
completely  away.  The  black  part  left  is  carbon  ;  this  would 
undergo  further  combustion  if  put  in  a  gas  flame  and  leave 
behind  a  further  small  amount  of  ash.  The  two  substances 
then  remaining  behind  in  the  burnt  part  of  the  stale  are 
carbon  and  ash  ;  one  black  and  combustible,  the  other  white, 
or  grey,  and  incombustible. 

Water  may  be  seen  on  both  head  and  stale  during  the 
combustion  of  a  match.  Its  source  may  be  from  the  damp- 
ness of  the  head,  or  of  the  stale,  but  there  is  a  small  quantity 
made  from  the  match  constituents  by  the  burning. 

These  changes  should  be  thoroughly  thought  out.  The 
match  consists  of  a  piece  of  wood  and  a  dry  paste  forming 
the  head.  The  blackness  of  head  and  stale  after  burning 
shows  that  carbon  is  in  the  original  paste  of  the  head,  and 
in  the  wood  of  the  stale.  Wood  contains  carbon,  despite 
the  difference  in  the  colour  of  the  two  things ;  it  is  present 
in  the  colourless  wood  and  heat  liberates  it. 

If  carbon  is  present  in  a  substance  heat  will  generally 
liberate  it,  and  then  if  heating  is  still  continued  the  carbon 
burns  to  the  invisible  gas  carbon  dioxide. 


QUESTIONS. 

1.  State  several  ways  by  which  heat,  without  light,  may  be  produced 
in  the  pit  by  rubbing  and  grinding. 

2.  State  all  the  ways  by  which  light,  accompanied  by  heat,  is  pro- 
duced in  the  pit. 

3.  Are  there  any  processes  going  on  in  the  pit  which  produce  heat 
alone  and  yet  cannot  be  placed  in  question  i  ? 

4.  Is  it  dangerous  to  rub  a  substance  which  is  an  inflammable  one  ? 
Give  an  example. 

5.  Which  do  you  think  is  more  likely  to  ignite  by  friction  :  sawdust 
or  wood,  damp  or  dry  paper  ?     Give  reasons. 

6.  How  may  it  be  proved  that  a  match  contains  carbon  ?    Describe 
an  experiment  to  show  that  carbon  often  exists  in  the  state  of  vapour. 


1 66          An  Introduction  to  Mining  Science. 

7.  Will  heat  be  produced  in  grinding  rock  to  form  stone  dust  for 
pits  ?    If  so,  how  do  you  explain  its  not  igniting  ?     Is  there  any  differ- 
ence in  the  inflammability  of  the  rock  and  its  dust  ? 

8.  Give  a  list  of  solid  and  liquid  substances  which  are  inflammable. 
What  objections  are  there  to  storing  them  in  a  pit  ? 


CHAPTER  X. 
THE  INFLAMMABILITY  OF  SUBSTANCES. 

THE  previous  chapter  has  brought  us  into  contact  with 
substances  which  when  made  hot  do  not  ignite,  yet  falling 
on  other  substances  finely  divided  these  are  ignited.  It  is 
plain  then  that  substances  vary  in  their  ease  of  ignition. 

Experience. 

The  heated  iron  used  in  laundry  work  must  when  not  actually 
in  use  be  resting  on  a  special  support  ;  if  it  were  left  on  the 
article  being  laundered,  e.g.  cotton  material,  ignition  might  occur. 
The  ignition-point  of  cotton  is  therefore  lower  than  that  of  iron 
or  steel.  A  hard  coal  is  more  difficult  to  ignite  than  a  soft  coal ; 
hence  the  latter  is  often  preferred  for  grate-fires  which  are  made 
daily. 

Iron  has  a  very  high  ignition-point,  the  fire  in  the  grate 
does  not  ignite  it,  but  most  of  us  have  seen  the  bright 
sparks  flying  from  the  iron  as  it  runs  molten  from  the 
furnace  or  as  it  flies  away  from  the  blacksmith's  anvil  as  he 
hammers  it  ;  in  either  case  the  particles  are  burning. 

The  ordinary  match  consists  of  substances  which  are 
easily  ignited,  but  yellow  phosphorus  is  even  more  easily 
ignited  than  a  match. 

There  are  substances  known  which  as  soon  as  they  come 
in  contact  with  the  air  burst  into  flame ;  their  ignition 
temperature  is  therefore  very  low.  There  are  some  substances 
in  the  gob  of  the  pit  which  easily  produce  heat ;  and  hence 
they  are  very  dangerous  owing  to  their  ease  of  breaking  into 
fire  and  flame. 

167 


1 68          An  Introduction  to  Mining  Science. 

Experiment, 

Throw  a  small  piece  of  calcium  phosphide  in  water  to  which 
a  small  quantity  of  hydrochloric  acid  has  been  added  ;  a 
spontaneously  inflammable  gas  is  liberated.  A  porcelain  dish  is 
a  convenient  vessel  to  use. 

Calcium  phosphide  receives  its  name  from  its  two  con- 
stituents :  calcium  and  phosphorus.  Compare  the  name 
calcium  carbide  with  that  of  the  substance  from  which  ace- 
tylene gas  is  obtained.  Calcium  is  a  metal  which  can  be  got 
out  of  lime  or  limestone ;  it  is  a  very  abundant  metal  in 
this  locked-up  state  ;  by  itself  it  is  not  very  useful  and 
therefore  is  not  very  common.  The  joint  action  of  water 
and  the  phosphide  ends  in  the  making  of  an  invisible  gas — 
composed  of  hydrogen  and  phosphorus — which  as  soon  as 
it  rises  through  the  water  surface,  and  therefore  comes  into 
contact  with  the  air,  ignites,  producing  white  fumes.  The 
white  fumes  are  not  the  gas  but  the  gas  burnt,  they  are 
oxide  of  phosphorus  formed  by  the  oxygen  of  the  air  and 
the  phosphorus  of  the  gas  uniting  together. 

The  foregoing  action  finds  a  practical  application  in  the 
apparatus  known  as  Holmes'  Signal 
Lights  for  marine  purposes.  This 
consists  of  a  tin  vessel  containing 
calcium  phosphide ;  it  has  a  tube 

FIG.   83.-Modei  of  a  PaSsinS  through    the   Bottom  of   the 

Holmes'  signal,  show-  can  an(i  a  small  hole  in  the  top  for 

ing  wooden  board  per-  the  gas  to  find  its  way  into  the  air. 

forated    by   a   vessel  The  board  in  which  the  can  is  fitted 

Ph°S"  forms  the  two  wooden  wi"gs  for  float- 
ing the  can.  When  the  appliance  is 
thrown  into  the  sea  water  finds  its  way  to  the  calcium 
phosphide,  and  the  gas  liberated  issues  out  of  the  jet ;  it 
ignites  itself  as  it  comes  in  contact  with  the  air. 

Experiment, 

Dissolve  a  bit  of  phosphorus  in  a  small  quantity  of  carbon  r* 
disulphide.     Pour  some  of  the  liquid  on  a  filter  paper  and  hang 
up  to  dry.     The  phosphorus  will  ignite. 

Rub  quickly  a  few  times  on  the  edge  of  the  bench  a  knife,  or 
warm  a  glass  rod  on  the  arm  of  your  coat  by  friction,  and  immedi- 


The  Inflammability  of  Substances.  169 

ately  touch  it  with  a  bit  of  dry  phosphorus.     Note  what  happens. 
Carry  out  both  these  experiments  far  from  any  flame. 

Carbon  disulphide  dissolves  phosphorus,  and  the  latter,  like 
all  other  substances  when  dissolved,  exists  in  a  very  finely 
divided  state  ;  finer  than  any  form  of  grinding  can  produce. 
Only  particles  of  gases  are  finer  than  the  particles  of  a 
liquid.  As  soon  as  the  liquid  disulphide  has  evaporated 
the  phosphorus  alone  is  left  on  the  surface  of  the  filter  paper ; 
owing  to  its  fineness  it  is  vigorously  attacked  by  the  oxygen  of 
the  air.  This  attack  results  in  the  production  of  heat  and 
the  phosphorus  fires.  In  the  second  experiment  the  heat 
necessary  to  start  the  combustion  is  derived  from  the  knife ; 
compare  this  with  the  first  experiment.  The  comparison  will 
teach  us  that  when  a  body  does  burst  into  flame  spon- 
taneously, it  has  before  doing  so  been  accumulating  heat  un- 
noticed by  us.  This  is  the  case  previous  to  the  sudden 
outburst  of  fires  in  the  gob. 

The  same  fumes  are  produced  here  as  in  all  cases  when 
a  substance  containing  phosphorus  burns,  they  are  always 
oxide  of  phosphorus. 

If  the  atmosphere  contained  sufficient  heat  at  a  high 
enough  temperature  it  would  at  once  ignite  the  phosphorus, 
as  the  warmed  knife  does,  and  phosphorus  would  be  spon- 
taneously inflammable.  When  phosphorus  does  ignite  in 
the  air  without  our  heating,  it  has  been  previously  accumulat- 
ing heat,  and  in  time  it  gains  enough  to  bring  it  to  its  ignition- 
point.  The  ignition-point  of  phosphorus  is  34°  C. 

Most  things  require  Warming  to  start  Burning, 

This  paper  is  combustible  and  the  air  around  it  is  a  sup- 
porter of  combustion.  Why  does  not  the  paper  burn  ?  It 
needs  warming  or  heating  to  a  certain  temperature  before 
the  action  between  the  air  and  paper,  called  burning,  begins. 
The  temperature  required  to  begin  the  action  is  called  the 
ignition  or  kindling-point  of  the  paper.  Compare  the  expres- 
sion with  the  similar  one  "boiling-point" — the  ideas  are 
much  the  same.  The  boiling-point  of  a  liquid  is  that  tem- 
perature at  which  bubbles  of  its  vapour  leaves  its  surface, 
e.g.  water  boils  at  212°  F.  or  1 00°  C.  The  idea  in  the  expres- 
sion is  therefore  the  temperature  of  the  water  when  it 
changes  from  liquid  to  steam.  The  idea  in  the  expression 


170          An  Introduction  to  Mining  Science. 

"  ignition-point  "  is  the  temperature  at  which  the  substance 
begins  to  burn.  Carbon  disulphide  has  for  its  ignition-point 
120°  C,  its  boiling-point  is  46°  C. 

If  the  temperature  at  which  a  body  ignites  is  near  to 
the  ordinary  temperature  of  the  air,  it  is  said  to  be  easily 
inflammable  and  its  ignition-point  is  represented  by  a  small 
number  of  degrees,  e.g.  phosphorus,  as  just  pointed  out, 
34°  C. 

A  substance  whose  ignition-point  is  far  above  the  tempera- 
ture of  the  air  will  have  a  big  number  to  represent  it,  e.g. 
marsh  gas  ignites  at  750°  C,  i.e.  a  temperature  7^  times  that 
of  boiling  water  is  necessary  to  start  its  combustion.  Now 
as  marsh  gas,  or  fire-damp,  may  be  ignited  by  a  spark,  it 
follows  that  the  temperature  of  the  spark  must  at  least  be 

750°  c. 

The  ease  of  "catching  fire"  varies  with  different  sub- 
stances ;  it  only  requires  a  low  temperature  to  start  a  match 
burning.  This  low  temperature  is  higher  than  the  air's  tem- 
perature, otherwise  a  match  would  be  spontaneously  inflam- 
mable, and  it  would  have  to  be  made  of  different  materials 
from  those  at  present  used. 

Experience, 

Consider  the  stages  in  the  burning  of  a  match.  The  head  con- 
sists of  easy  inflammable  material  which  is  ignited  by  the  small 
amount  of  heat  produced  by  friction.  The  stick  of  the  match  is 
thin  and  dry  so  that  it  may  easily  catch  fire  from  the  quickly 
burning  head.  In  order  to  make  certain  of  the  stick  catching  fire 
several  makes  of  matches  have  their  sticks  dipped  into  a  com- 
bustible material  such  as  molten  paraffin  wax. 

Substances  are  used  in  the  match -head  which  have  a  low 
ignition-point,  and  on  striking  its  flame  hands  on  the  com- 
bustion to  the  wood  which  has  a  high  ignition-point. 

The  match  illustrates  the  grading  of  things  according  to 
their  ease  of  inflammability  and  combustibility,  in  order  to 
give  ease  at  the  starting  of  the  burning  and  then  a  flame 
lasting  for  a  few  seconds.  This  few  seconds  is  quite  suffi- 
cient to  reach  the  ignition-point  of  other  things,  e.g.  gas, 
fires,  cigars,  etc. 


The  Inflammability  of  Substances.  I /I 

Experiment, 

Place  a  small  amount  of  carbon  disulphide  in  a  porcelain  £ 
dish.  Light  a  Bunsen  burner  ;  keep  it  far  away  from  the  carbon 
disulphide.  Heat  slightly  a  glass  rod  in  the  burner  and  then 
hold  it  over  the  disulphide  ;  if  the  vapour  does  not  ignite  in- 
crease the  temperature  of  the  rod  until  the  vapour  does  ignite. 
Turn  on  the  tap  of  another  Bunsen  and  try  to  light  the  gas  by 
a  hot  rod.  A  temperature  of  about  700°  C. — bright  red  heat — 
will  ignite  the  gas. 

A  variation  of  this  experiment  is  to  try  to  ignite  both  disulphide 
and  gas  with  a  glowing  piece  of  wood  ;  it  will  fail  in  the  case  of 
the  gas. 

Or  two  gas  cylinders  may  be  filled  one  with  coal  gas  and  one 
with  carbon  disulphide  vapour — a  drop  or  two  of  the  liquid  will 
soon  fill  the  cylinder — and  the  heated  rod  introduced  into  each. 

Carbon  disulphide  boils  at  46°  C.,  a  low  temperature  for 
a  liquid  to  boil,  and  the  result  is  that  it  is  very  quickly  con- 
verted into  a  vapour.  The  vapour  is  a  heavy  one,  and 
therefore  does  not  quickly  get  away.  As  the  liquid  turns 
into  vapour  it  becomes  mixed  with  the  surrounding  air  and 
it  may  then  be  ignited  by  a  hot  rod,  at  a  temperature  of  about 
120°  C. ;  this  temperature  is  therefore  its  ignition-point. 
If  a  liquid  is  easily  converted  into  vapour  which  is  combus- 
tible, then  the  liquid  is  a  dangerously  inflammable  one. 

The  following  experiment  may  be  performed  with  the  or- 
dinary incandescent  mantle  burner. 

Experiment, 

Turn  on  and  light  the  gas,  and  allow  the  mantle  to  get 
thoroughly  hot.  Now  quickly  turn  out  the  gas  and  whilst  the 
mantle  is  bright  red  hot,  turn  on  the  gas  :  it  will  ignite.  If  the 
mantle  is  allowed  to  go  to  a  dark  red  heat,  the  gas  will  not  re- 
ignite. 

The  ignition-point  of  coal  gas  is  very  much  higher  than 
that  of  carbon  disulphide,  it  is  said  to  be  from  650°  C.  to 
700°  C. 

Experiment, 

Place  a  small  quantity  of  paraffin  oil  in  a  porcelain  dish 
and  try  to  ignite  the  oil  with  a  lighted  match.  It  will  not  ignite. 
Place  the  dish  on  a  tripod  as  shown  in  Fig.  84  and  warm  gently, 


1/2          An  Introduction  to  Mining  Science. 


applying  a  light  to  see  if  the  vapour  ignites.  If  the  temperature 
of  the  oil  were  taken  when  the  vapour  just  ignites  the  point  of 
ignition  is  obtained. 

The  fact  that  oil  cannot  be  ignited  on  the  surface  pre- 
viously to  warming  is  due  to  two  things,  an  insufficient 
amount  of  vapour  is  coming  off  and  it  is  at  too  low  a  tem- 
perature. 

As  the  oil  is  warmed  the  vapour  particles  over  the  surface 
get  more  and  more  numerous  and  their  temperature  higher, 
and  also  the  air  particles ;  in  this  way  an  explosive  mixture 
is  formed  and  there  is  a  flash  when  the  light  is  applied. 

Imagine  that  the  mixture  of  air  and  vapour  particles  is 
formed  in  the  reservoir  of  an  oil  lamp,  then  if  the  mixture 
becomes  hot  enough  it  ignites  and  the  vessel  is  shattered : 
the  explosion  is  a  dangerous  one.  When  the  mixture  is 
fired  in  an  open  space,  as  in  the  experiment,  there  is  no 
danger,  and  no  damage  will  result  if  caution  is  observed. 
The  comparison  brings  out  the  difference  between  firing  a 
mixture  of  air  and  inflammable  gas  in  closed  and  open 
spaces.  In  the  open  air  the  heat  of  the  firing  drives*  apart 
the  air,  as  a  flash  of  lightning  does  in  cutting  its  way  through, 

but  it  joins  again  and  is  un- 
broken. In  the  closed  space 
the  heat  of  the  firing  drives  the 
air  against  a  wall  of  some  type, 
and  unless  it  is  extremely  strong 
the  wall  is  shattered. 

Flash-point  of  Kerosene. 

Imbed  a  porcelain  dish  in  sand 
on  a  tin  lid  or  a  sandbath  and 
place  on  a  tripod  (see  Fig.  84). 
Fill,  almost,  the  dish  with  kero- 
sene and  hang  a  thermometer  into 
the  oil,  suspending  it  from  the  ring 
of  a  retort  stand. 

Raise  the  temperature  of  the 
oil  slowly,  about  6°  per  minute, 
with  a  small  flame.  Occasionally 
pass  a  flame  over,  and  £  in.  above,  the  surface  of  the  oil.  Read 
the  thermometer  when  there  is  a  flash  ;  the  number  of  degrees 
registered  is  the  flash  or  ignition-point. 


:o 


FIG.  84. — Apparatus  for  find- 
ing the  flash-point  of  a 
liquid. 


The  Inflammability  of  Substances.  173 

Allow  the  liquid  to  cool  slightly  and  repeat  the  experiment 
for  a  corroboration  of  the  flash-point  obtained. 

Heat  is  produced  each  time  the  vapour  is  flashed  and 
this  affects  the  thermometer,  so  care  should  be  taken  not 
to  read  the  temperature  when  the  thermometer  is  affected 
by  the  heat  of  the  flash.  It  is  therefore  advisable  to  notice 
the  temperature  just  before  an  attempt  to  flash  the  vapour 
is  made. 

The  temperature  of  the  vapour  just  before  it  ignites  will 
be  the  same  as  the  liquid  in  the  dish,  this  temperature  is 
the  flash-point. 

The  flash-point  is  an  index  of  the  dangerous  nature  of 
the  oil ;  if  the  flash-point  is  low  it  is  a  dangerous  oil,  if 
high  it  is  not  so  dangerous.  The  danger  comes  from  the 
ease  of  the  vapour  flashing  and  producing  an  explosion  if 
in  a  confined  place,  e.g.  a  lamp. 

If  the  ignition-points  of  coal  gas  or  fire-damp  were  higher 
than  they  are — 650°  C.  and  750°  C.  respectively — it  would  be 
more  difficult  to  produce  an  explosion  either  in  a  house  or 
in  a  mine.  Paraffin  oil  is  required  to  have  a  flash-point  of 
not  less  than  73°  F.  (227°  C. )  ;  the  requirement  should  be  as 
high  as  ioo°F.  A  low-flash  point  is  a  great  danger;  it 
was  a  greater  danger  several  years  ago  when  petrol  was 
not  separated  from  petroleum,  as  it  is  now,  and  many 
disastrous  lamp  explosions  occurred  in  houses.  The  de- 
mand for  petrol  has  resulted  in  the  separation  of  it  from 
petroleum,  and  so  the  constituent  of  petroleum  which  has 
a  low  flash-point  has  been  removed.  In  this  way  the 
coming  of  the  petrol  engine  has  reduced  the  risk  of  a 
lamp  explosion. 

Experience. 

Search  out  the  instructions  given  on  labels  to  avoid  the  difficul- 
ties and  dangers  in  connection  with  the  storage  of  small  quantities 
of  inflammable  liquids,  e.g.  a  bottleful  of  methylated  spirit,  ben- 
zoline,  naphtha,  etc. 

Their  catching  fire  is  connected  with  the  ease  that  they 
give  off  a  vapour,  and  the  danger  of  bringing  a  vessel  full 
near  the  fire  is  owing  to  the  likelihood  of  air  mixing  with 
their  vapour  in  the  storage  vessel,  be  it  bottle  or  tank,  and 


174          An  Introduction  to  Mining  Science. 

then  exploding.  It  would  be  an  explosion  in  a  confined 
space  and  so  likely  to  be  disastrous. 

Vapours  and  gases  consist  of  very  small  particles,  of  such 
a  degree  of  fineness  that  we  cannot  form  an  adequate  idea 
of  it;  hence  they  are  in  the  right  condition  for  quick  com- 
bustion, i.e.  for  exploding. 

That  fineness  or  thinness  makes  the  beginning  of  com- 
bustion easy  is  again  illustrated  by  the  ease  with  which 
shavings  burn  compared  with  that  of  wood.  All  the  fore- 
going facts  help  to  show  that  the  fineness  of  division  of  coal 
dust  in  the  mine  is  no  doubt  the  chief  factor  in  starting  a 
coal-dust  explosion,  and  it  may  not  always  require  the  same 
temperature  to  do  it. 

Experiment. 

Take  a  tin  lid  and  place  in  it  some  finely  divided  iron,  known 
as  "  reduced  iron,"  then  hold  it  over  the  Bunsen  burner.  Notice 
that  the  iron  burns  very  easily.  Drop  a  bit  of  the  iron  in  the 
Bunsen  flame  ;  it  will  burn. 

Iron  in  the  solid  state,  e.g.  girders  or  other  iron  struc- 
tures, is  used  because  it  does  not  burn,  a  temperature  16 
to  1 8  times  that  of  boiling  water  is  even  required  to  melt  it. 
Fineness  of  division  therefore  helps  the  ease  of  combustion 
of  iron ;  it  is  also  shown  by  the  brilliancy  of  the  hot  sparks 
that  fly  from  the  smith's  anvil. 

There  is  plenty  of  evidence  in  the  pages  of  this  book  to 
show  that  fineness  of  division  is  conducive  to  inflammability. 

The  influence  of  fineness  of  division  on  the  combusti- 
bility of  coal  is  well  shown  by  experiments  which  gave 
these  results : — 

In  bits  of  coal  not  less  than  half  an  inch  in  size  they  did 
not  take  fire  below  850°  F.  Dust  composed  of  bits  about 
^\  of  an  inch  in  size  took  fire  at  425°  F.,  but  coal  in  a  very 
fine  powder  took  fire  at  212°  F.,  i.e.  the  temperature  of 
boiling  water,  the  coal  being  exposed  to  air  heated  to  the 
temperature  stated. 

Practical  Application  to  Mining, 
Most  miners  have  noticed  that  a   safety  lamp  is   more 
easily  lighted  when  the  wick  is  warm  than  when  it  is  cold ; 


The  Inflammability  of  Substances.  175 

4 

this  is  particularly  noticeable  when  the  lamp  is  lit  electric- 
ally. 

Those  who  have  used  safety  lamps  burning  naphtha  or 
benzine  will  probably  have  noticed  that  they  light  much 
more  easily  than  lamps  burning  colza  or  paraffin.  Owing 
to  their  low  ignition-point  naphtha  and  benzine  must  be 
stored  in  the  lamp-room  in  a  special  manner  in  order  to 
prevent  them  taking  fire.  A  method  of  doing  this  is  to 
connect  up  the  storage  tank  to  a  cylinder  of  carbon-dioxide 
instead  of  allowing  it  to  be  open  to  the  atmosphere.  When 
spirit  is  drawn  out  of  the  tank  carbon  dioxide  instead  of  air 
takes  its  place,  and  thus  prevents  the  possibility  of  an 
explosive  or  combustible  mixture  being  formed. 

Oil  is  used  in  the  pit  for  various  purposes,  and  accidents 
have  been  caused  by  it  becoming  ignited. 

In  South  Wales  a  fatal  accident  was  caused  by  the  apron 
of  a  lamp  cleaner  catching  fire  from  an  open  grate  in  the 
lamp- room. 

In  the  North  of  England  a  serious  underground  fire  was 
caused  by  a  paraffin  lamp  used  for  heating  the  carburetter 
of  an  oil  engine  catching  fire.  The  oil  for  the  engine  was 
supplied  from  a  tank  at  the  surface,  having  a  capacity  of 
320  gallons,  through  a  j  inch  pipe,  and  the  whole  contents 
ran  to  the  engine  and  increased  the  fire. 

In  Scotland  a  serious  and  fatal  underground  fire  was 
caused  by  oil  in  the  box  of  the  controller  of  an  electric 
motor  becoming  ignited.  There  were  only  two  men  in  the 
pit  and  the  smoke  did  not  reach  their  working  place,  but 
at  the  end  of  the  shift  as  they  were  coming  outbye  towards 
the  shaft  they  met  the  smoke  coming  in  towards  them. 
They  stopped  and  consulted  as  to  what  they  should  do, 
and  finally  decided  to  try  and  get  through  the  smoke  by 
the  intake,  and  the  younger  man  did  so  safely,  but  the  other, 
who  was  57  years  of  age,  was  overcome,  and  when  found 
was  dead.  The  management  thought  that  the  fumes  from 
the  oil  passing  over  the  top  of  the  fuses  were  ignited  by 
a  fuse  blowing.  Another  theory  was  that  a  short-circuit 
occurred  between  the  terminals  inside  the  box  just  above 
the  oil  and  this  set  fire  to  the  oil. 

Reference  has   been    made   earlier   in   this   chapter   to 


176          An  Introduction  to  Mining  Science. 

"  spontaneous  ignition  ".     A  very  important  class  of  mine 
fires — gob  fires — are  due  to  this  cause. 

Cause  of  Gob  Fires, 

Probably  the  principal  cause  is  the  heating  set  up  by  the 
coal,  left  in  the  gob  or  goaf,  absorbing  oxygen  from  the 
air.  Once  this  action  is  started  under  favourable  conditions, 
the  temperature  gradually  increases  until  the  point  of  igni- 
tion of  the  coal  is  reached.  One  of  the  first  signs  of  a  gob 
fire  is  the  appearance  of  moisture  on  props  and  packs.  This 
is  called  "sweating".  The  next  sign  is  a  smell  resembling 
that  of  paraffin  or  petrol,  which  is  followed  by  the  true  "gob 
stink,"  a  characteristic  smell  which  it  is  not  easy  to  describe. 

Fires  due  to  spontaneous  ignition  may  occur  in  pillars 
of  coal,  near  faults,  or  in  the  waste  or  gob  from  which  the 
coal  has  been  worked. 

How  to  Deal  with  a  Gob  Fire, 

A  gob  fire  may  be  dealt  with  by  building  stoppings  round 
it  and  so  excluding  the  air ;  by  the  use  of  inert  gas  such  as 
nitrogen  or  carbon  dioxide,  or  by  driving  roads  to  the  fire, 
filling  it  into  tubs  and  sending  it  out  of  the  pit.  The  method 
of  filling  out  the  fire  is  probably  the  best  one,  particularly 
in  a  mine  worked  on  the  Longwall  System.  The  source 
of  danger  is  entirely  removed,  and  if  the  fire  is  tackled  in 
its  early  stages  the  difficulties  to  be  overcome  are  not  too 
great. 

Fig.  85  shows  the  method  of  driving  roads  or  "  scourings  " 
to  a  fire  in  the  goaf  of  a  Longwall  working.  When  the  fire 
is  reached  sand  is  thrown  on  to  it  and  it  is  filled  into  tubs 
of  iron  or  steel.  Sometimes  a  single  scouring  is  driven 
which  is  ventilated  by  means  of  metal  air  pipes  which  are 
not  liable  to  take  fire. 

When  a  pair  of  scourings  are  driven  they  are  ventilated 
by  means  of  air  pipes  until  a  connexion  can  be  made  be- 
tween them  when  the  ventilation  takes  the  path  shown  in 
figure. 

The  roof  of  the  scouring  may  be  supported  by  steel 
girders,  the  spaces  between  them — if  the  roof  requires  it 


The  Inflammability  of  Substances.  177 

— being  filled  in  with  metal  plates  resting  on  the  girders. 
It  is  advisable  to  spread  stone  dust  freely  in  the  neighbour- 


1V__  *\V_.  ___\VJ 


FIG.  85. — Showing  a  pair  of  scourings  driven  to  a  gob  fire. 

hood  of  the  fire  with  the  object  of  preventing  an  explosion 
of  fire-damp — if  one  should  occur — from  spreading  to  other 
parts  of  the  mine. 

Prevention  of  Gob  Fires, 

To  prevent  gob  fires  air  must  not  be  allowed  to  enter  the 
gob.  Airways,  both  intake  and  return,  should  be  large  so 
as  to  make  the  difference  in  pressure  between  the  intake 
and  return  as  small  as  possible,  and  in  this  way  prevent  the 
air  short-circuiting  through  the  gob.  In  gate  roads  roof  may 
be  taken  down  and  the  packs  buried,  and  old  gate  roads 
which  are  out  of  use  may  be  packed  off  with  sand  and 
stone. 

Hydraulic  storage  is  highly  recommended  in  some 
quarters  as  a  means  of  preventing  gob  fires.  The  coal 
taken  out  of  the  mine  is  replaced  by  material  from  the 
surface,  such  as  sand,  gravel,  stone  or  any  cheap  non- 
combustible  material.  This  material  is  ground  up  and 
washed  down  pipes  which  lead  to  the  part  of  the  gob 
requiring  filling.  The  solid  matter  remains  in  the  gob  and 
the  water  is  pumped  back  to  the  surface  and  used  over 
again. 

12 


1/8  An  Introduction  to  Mining  Science. 

Many  advantages  are  claimed  for  this  system,  but  it 
has  not  yet  been  adopted  in  this  country  to  any  great 
extent. 

QUESTIONS. 

1.  Which  is  the  more  easily  burnt,  a  heap  of  sawdust  or  one  of  shav- 
ings ?     Does  the  conclusion  warrant  you  in  saying  the  finer  the  sub- 
stance is  the  easier  its  combustion  ?     If  not,  how  do  you  explain  any 
contradiction  ? 

2.  Consider  the  similar  difficulty,  as  in  Question  I,  in  connexion 
with  a  heap  of  coal  and  coal  dust.     Give  explanations. 

3.  Why  should  gunpowder,  or  the  powder  used  in  fireworks,  be  a 
finely  divided  substance  ? 

4.  Do  you  think  a  small  charge  of  gunpowder  could  be  placed  in 
the  same  position  and  with  the  same  result  as  the  match  in  Fig.  77, 

P-  153  ? 

5.  Draw  up  a  list  of  inflammable  substances  found  in  pits. 

6.  Draw  up  a  list  of  inflammable  liquids  known  by  experiment  and 
experience ;  try  to  arrange  them  according  to  their  degree  of  inflamma- 
bility and  give  reasons  for  your  so  doing. 

7.  Find  out  and  describe  the  manner  in  which  inflammable  liquids 
are  stored  in  the  lamp-room  of  your  pit.     Give  reasons  for  the  method 
adopted. 


CHAPTER  XI. 
SUBSTANCES  CONTAINING  FIXED  OXYGEN. 

WE  have  learnt  that  nitrogen  and  oxygen  exist  in  the  air  and 
almost  form  the  whole  of  it :  see  the  Table  of  Composition 
given  on  p.  37.  Between  these  two  constituents  there  is 
no  bond  of  union,  each  particle  of  oxygen  exists  indepen-. 
dently  of  each  particle  of  nitrogen.  Now  although  nitrogen 
is  the  largest  in  amount  it  is  not  of  so  much  importance 
as  oxygen  on  account  of  the  activity  of  the  latter.  The 
activity  of  oxygen  and  the  inactivity  of  nitrogen  is  well  illus- 
trated by  the  experiment,  given  on  p.  22,  for  the  separation 
of  nitrogen  from  the  air.  Phosphorus  is  used  because  it 
and  oxygen  actively  attack  each  other;  it  is  a  substance 
which  put  in  the  air  draws  the  oxygen  particles  to  it  and  then 
holds  them  firmly  and  securely.  Now  although  this  is  the 
case  with  phosphorus  and  oxygen,  nitrogen  and  oxygen 
even  at  the  high  temperature  of  burning  phosphorus  do  not 
attack  each  other  together. 

In  the  presence  of  an  electric  flame  of  about  3500°  C. 
temperature,  nitrogen  and  oxygen  particles  of  the  air  attack 
each  other,  enter  into  union,  and  this  united  product  of 
oxygen  and  nitrogen,  called  oxide  of  nitrogen,  attacks  the 
water  present  in  the  air  and  forms  an  acid.  On  account 
of  its  containing  nitrogen  this  acid  is  called  nitric  acid,  but 
its  most  important  constituent  is  oxygen. 

Nitric  acid  is  a  very  active  acid,  most  substances  being 
attacked  by  it ;  in  such  actions  new  substances  are  produced. 

Experiment, 

Dry  over  the  Bunsen  burner  (preferably  in  a  draught  cup- 
board)  a  small  quantity  of  sawdust  in  a  sand  tray.  When  the 

179  12  * 


i8o          An  Introduction  to  Mining  Science. 


dust  begins  to  char  and  shows  patches  of  bright  red  take  away 

the  burner  and  drop  on  it, 
drop  by  drop,  strong  nitric 
acid  ;  notice  the  incandes- 
cence, possibly  flame  is  pro- 
duced. 

An  old  tin  lid  will  do  for 
the  carrying  out  of  the  ex- 
periment. 

This  vigorous  combus- 
tion shows  that  heat  is 
produced,  but  the  pro- 
duction of  carbonic  acid 
gas  is  lost  sight  of  owing 
to  its  being  colourless. 
Red  fumes  which  tell  us 
we  are  dealing  with  nitric 

FIG.  86  -Apparatus  for  heating  saw-       acid  wil1  be  .Seen"       This 
dust  on  an  iron  tray.  experiment   is   very    im- 

portant because  it  shows 

the  burning  power  of  bound  oxygen.  It  is  necessary  that  we 
should  learn  some  further  properties  of  nitric  acid,  therefore 
perform  the  following  experiment. 

Experiment, 

Place  a  bit  of  copper,  a  shaving  or  a  turning,  in  a  test  tube, 
and  then  add  a  few  drops  of  strong  nitric  acid.  Changes  are 
at  once  seen  ;  red  fumes  are  given  off,  a  green  solution  is  formed, 
and  the  liquid  becomes  hot. 

It  should  be  carefully  noticed  that  the  action  starts  with- 
out any  heat. 

All  that  goes  on  is  not  seen,  but  the  red  gas  spoken  of 
above  is  the  oxide  of  nitrogen ;  it  is  driven  off  from  some  of 
the  nitric  acid.  The  green  solution  contains  the  copper 
which  has  been  dissolved  by  some  of  the  nitric  acid.  This 
green  substance  is  called  nitrate  of  copper  ;  its  name  em- 
phasizes its  formation  from  nitric  acid  and  copper,  and  also 
tells  its  composition.  The  aim  of  scientific  names  is  to 
tell  something  of  the  components  of  a  substance. 


Substances  Containing  Fixed  Oxygen.         181 
Experiment, 

A  few  drops  of  nitric  acid  evaporated  in  a  porcelain  dish  gives 
off  red  fumes  and  leaves  no  residue  ;  it  is  entirely  a  liquid. 

If,  on  the  other  hand,  the  green  solution  called  nitrate  of 
copper  is  placed  in  the  dish  and  the  liquid  slowly  evaporated 
a  green  solid  would  remain ;  this  is  solid  nitrate  of  copper, 
the  copper  having  fixed  some  nitric  acid. 

Substances  made  from  Nitric  Acid. 
Experiment, 

How  to  make  a  solid  substance  called  nitrate  of  potash. 
Place  in  a   porcelain  dish  a  small   piece  of  caustic  potash, 
about  the  size  of  a  pea,  and  add,  drop  by  drop,  dilute  nitric  acid, 


=0 


FIG.  87. — Apparatus  for  evaporating  away  water  from  a  dissolved 
substance. 

until  the  potash  has  dissolved  and  the  solution  after  well  stirring 
turns  blue  litmus  paper  red.  Now  evaporate  off  all  the  liquid 
over  the  Bunsen  flame,  moving  the  flame  about  as  the  liquid  gets 
pasty.  Finally  it  becomes  dry  and  a  white  solid  is  obtained. 


1 82  An  Introduction  to  Mining  Science. 

If  the  new  substance  is  to  have  a  scientific  name,  one 
denoting  its  constituents,  it  should  be  called  nitrate  of 
potash,  the  word  nitrate  denoting  its  nitric  acid  part. 

Nitrate  of  potash  is  very  different  from  its  two  constituents, 
it  is  a  neutral  substance.  The  caustic,  i.e.  the  corrosive 
property  of  the  potash  as  well  as  the  acidity  of  the  acid  are 
lost.  Nitrate  of  potash  is  used  for  preserving  food  from  decay, 
and  in  making  gunpowder  and  other  explosives.  The  new 
substance  is  that  popular  and  familiar  substance  saltpetre ; 
"  villainous  saltpetre  "  as  it  is  often  called ;  get  a  specimen 
and  taste  it. 

Experiment. 

Take  some  nitrate  of  potash  and  powder  it,  then  mix  with  some 
powdered  charcoal.  Place  a  small  quantity  of  the  mixture  in  a 
dry  test  tube,  hold  the  tube  away  from  the  face  and  heat  care- 


FIG.  88.— Method  of  heating  a  small  quantity  of  a  substance  in  a 
test  tube. 

fully.     A  fierce  action  goes  on  and  sparks  of  red-hot  charcoal 
are  formed. 


Substances  Containing  Fixed  Oxygen.          183 

The  burning  of  the  charcoal  is  due  to  its  being  attacked  by 
oxygen  of  the  nitrate,  forming  carbonic  acid  gas.  Nitrates 
are  ready  to  attack  most  things  when  they  are  warmed  in 
their  presence.  The  mixture  is  only  one  constituent  short 
of  being  gunpowder. 

Experiments  on  Nitrates,  etc. 

In  all  the  following  experiments  use  a  small  quantity  of  the 
substance,  hold  the  tube  with  the  glowing  splinter  just  in  the 
mouth  of  the  tube  and  away  from  the  face. 

Heat  strongly  over  the  Bunsen  flame  in  a  dry  test  tube  any 
one  of  the  following  nitrates  :  nitrate  of  potash,  nitrate  of  lead. 
Detect  the  oxygen  as  it  is  liberated  by  a  glowing  splint  of  wood 
which  will  burst  into  flame. 

Repeat  the  foregoing  with  chlorate  of  potash  and  oxide  of  lead 
separately  heated  in  a  test  tube. 

Nitrate  of  ammonia  may  be  heated  strongly  ;  it  is  slightly  ex- 
plosive and  will  set  a  glowing  splinter  aflame. 

It  may  be  difficult  to  drive  off  much  oxygen  from  the 
nitrate  of  potash,  but  nitrate  of  lead,  oxide  of  lead,  and 
chlorate  of  potash  easily  give  off  the  gas.  We  have  learnt 
that  nitrate  of  potash  easily  attacks  charcoal,  and  this  it  does 
by  its  oxygen  coming  off  easily  in  the  presence  of  the 
charcoal. 

Experiment  on  the  Combustion  of  a  Substance  by  its 
own  Oxygen. 

Heat  a  small  quantity  of  dichromate  of  ammonia  in  a  dry  test 
tube  and  notice  the  red  heat  produced  by  its  combustion. 

Very  vigorous  combustion  goes  on,  and  after  its  starting 
the  tube  may  be  withdrawn  from  the  flame  but  com- 
bustion continues.  If  air  were  excluded  by  a  layer  of  sand 
over  the  substance,  combustion  would  still  proceed  easily. 

Oxygen  containing  Substances. 

An  explanatory  note  on  some  of  the  substances  just  used 
will  help  to  form  exact  ideas  of  them. 

Nitrates  are  substances  made  from  nitric  acid  and  a  metal 
or  other  substance ;  they  are  very  rich  in  oxygen. 


184          An  Introduction  to  Mining  Science. 

The  word  oxide  denotes  a  substance  which  contains 
oxygen  and  another  substance,  e.g.  oxide  of  lead.  An 
oxide  o.f  lead  is  used  by  plumbers  under  the  name  of  "  red 
lead  ";  it  contains  90-6  per  cent  of  lead  and  9-4  per  cent 
of  oxygen.  On  heating  it  gives  off  some  of  its  oxygen  and 
changes  to  a  yellowish  oxide  containing  92-8  per  cent  of  lead 
and  7-2  per  cent  of  oxygen.  A  brown  lead  oxide  contains 
13*4  per  cent  of  oxygen  and  the  remainder  is  lead. 

Chlorate  of  potash  and  dichromate  of  ammonia  are  very 
rich  in  oxygen;  it  may  be  said  that  their  names  do  not 
declare  this  fact  to  you.  To  a  chemist  the  names  do, 
because  words  denoting  chemicals  ending  in  -ate,  or  plural 
-ates,  signify  there  is  oxygen  in  them.  The  parts  chlor  and 
chrom  of  the  words  mean  there  are  substances  in  them 
known  as  chlorine  and  chromium,  the  former  a  gas,  the 
latter  a  metal.  It  is  plain  therefore  that  the  mentioned 
substances  chlorate  and  chromate  contain  three  things  each. 

Glycerine  Nitrate. 

The  last  nitrate  we  shall  study  is  often  called  "nitro- 
glycerine "  ;  it  is  one  of  the  best-known  constituents  of 
explosives.  Dynamite  contains  75  percent  of  it. 

Experiment. 

Make  a  mixture,  in  a  test  tube,  of  one  drop  of  strong  nitric  and 
four  drops  of  strong  sulphuric  acid.  Cool  it  well  under  the  tap 
by  allowing  water  to  run  on  the  outside  of  the  tube.  Add  one 
drop  of  glycerine  to  the  acid  mixture.  Pour  the  solution  obtained 
into  another  test  tube  half  full  of  water.  Nitro-glycerine  sepa- 
rates out  as  fine  globules  of  a  heavy  whitish  oil. 

When  the  oil  has  been  seen  and  identified  pour  all  the  mixture 
down  a  drain  and  then  allow  the  tap  to  run  for  a  few  seconds. 

The  sulphuric  acid  simply  helps  the  nitric  acid  to  attack 
the  glycerine ;  the  changes  in  the  properties  of  glycerine 
after  it  has  become  altered  into  glycerine  nitrate  are  worth 
noticing.  Glycerine,  which  is  so  well  known,  is  a  thick 
liquid  heavier  than,  and  soluble  in,  water.  It  is  sweet  and 
not  explosive.  Glycerine  nitrate  is  insoluble  in  water  and 
explosive.  These  changes  are  a  further  lesson  in  chemistry  ; 
the  science  that  shows  that  when  a  body  changes  or  adds 
to  its  original  constituents  it  changes  its  qualities  or  pro- 


Substances  Containing  Fixed  Oxygen.         185 

perties.  In  order  to  show  how  largely  and  widely  nitrates  are 
used  in  the  making  of  explosives,  the  following  examples 
may  be  considered.  They  are  taken  from  the  explosives 
in  the  Coal  Mines  Order  of  7  April,  1914  : — 

Commercial  Name  Percentage  by 

of  Explosive.  Weight  Present. 

Abelite,  No.  i     Nitrate  of  Ammonia,  70  per  cent. 
Arkite  .         .     Nitrate  of  Glycerine,  33  per  cent. 

Nitrate  of  Potash,  28  per  cent. 
Duxite  .         .     Nitrate  of  Glycerine,  33  per  cent. 

Nitrate  of  Soda,  29  per  cent. 
Excellite        .     Nitrate  of  Glycerine,  6  per  cent. 

Nitrate  of  Ammonia,  50  per  cent. 

Nitrate  of  Potash,  2 1  per  cent. 

Speed  of  Travelling  of  an  Explosion. 

Make  a  narrow  train  of  gunpowder  on  a  long  board.  Ignite 
at  one  end  and  take  the  time  for  the  ignition  to  travel  to  the  other 
end.  Calculate  the  speed  in  feet  per  minute.  Notice  the  differ- 
ence between  the  unburnt  and  burnt  states  of  the  powder. 

In  a  particular  experiment  the  train  was  5  feet  long,  the 
time  of  travelling  from  end  to  end  4  seconds.  Hence  the 
speed  is  75  feet  per  minute. 

The  smoke  which  is  produced  by  the  combustion  should 
be  noticed  inasmuch  as  it  quickly  rises  to  the  ceiling  of  the 
room  and  then  slowly  falls  again.  Why  does  it  do  so  ? 

Checking  the  Speed  of  the  Explosion, 

Make  a  similar  train  to  the  first  one  and  then  sprinkle  stone 
dust,  or  fine  sand,  on  its  surface.  Ignite  the  train  and  take  the 
time  of  passing  of  the  ignition  wave  from  one  end  to  the  other. 

In  the  particular  case  above  mentioned  it  was  found  that 
the  time  was  increased  by  sand  to  8  seconds,  hence  the 
velocity  had  been  reduced  to  37-^  feet  per  minute. 

Compare  this  action  with  the  addition  of  incombustible 
material  to  flannelette  in  order  to  render  the  latter  less  in- 
flammable. 

In  some  further  experiments  to  find  the  influence  of  leav- 
ing gaps  in  the  train  of  powder  and  of  mixing  it  with  stone 


1 86          An  Introduction  to  Mining  Science. 

dust  obtained  from  collieries,  the  following  facts  were  ob- 
tained : — 

With  gaps  at  least  a  half  inch  in  length  the  speed  of 
ignition  along  the  train  was  increased ;  it  is  plain  therefore 
that  the  ignition  jumps  across  a  gap  quicker  than  it  travels 
through  the  train,  the  time  was  only  3  seconds.  It  was 
found  that  a  mixture  of  stone  dust  and  gunpowder  in  the  pro- 
portion of  3  cubic  inches  of  the  former  and  one  of  the  latter, 
laid  as  a  train  would  not  ignite. 

A  mixture  of  one  part  of  each  constituent  ignited. 

The  Explosive  Force  of  Gunpowder. 

Gunpowder,  which  consists  of  sulphur,  nitrate  of  potash, 
and  charcoal,  must  be  a  very  uniform  mixture,  or  it  would  not 
burn  instantaneously,  i.e.  explode.  The  substances  must 
also  be  finely  divided,  then  it  will  quickly  fire  when  once 
ignited. 

Gunpowder  burnt  in  the  open  air  has  no  explosive  force, 
but  shows  interesting  effects.  Much  white  smoke,  i.e.  well- 
burnt  smoke,  and  invisible  gases  are  produced :  carbon 
dioxide,  carbon  monoxide,  nitrogen,' and  a  small  amount  of 
marsh  gas.  Despite  the  fact  that  the  smoke  contains  gases 
heavier  than  air  a  great  cloud  rises  up  at  a  good  speed  owing 
to  the  heat  produced  expanding  the  gases  and  making  them 
very  light.  As  the  smoke  cools  it  falls  down  to  the  floor. 

At  the  Chicago  Exhibition  a  Krupp  cannon  was  exhibited 
which  when  fully  charged  could  hold  253  Ib.  of  gunpowder. 
When  fired  it  could  throw  a  shot  of  473  Ib.  weight  a  distance 
of  twelve  miles  ;  the  shot  in  rising  attained  the  great  height 
of  four  miles. 

The  force  required  to  hurl  this  ball  came  entirely  from  the 
great  bulk  of  gas  which  was  produced  by  the  quick  combus- 
tion of  the  gunpowder. 

Practical  Application  to  Mining, 

Many  attempts  have  been  made  by  the  use  of  the  lime 
cartridge  and  mechanical  wedges  of  various  designs  to 
abolish  explosives  from  our  mines,  but  so  far  they  have  not 
met  with  success. 


Substances  Containing  Fixed  Oxygen.         187 

Explosives  are  largely  used  in  the  driving  of  stone  drifts 
and  in  many  cases  in  getting  the  coal  and  ripping  the  gate 
roads.  Between  40,000,000  and  50,000,000  shots  are  fired 
annually  in  the  mines  of  this  country,  the  amount  of  ex- 
plosive used  being  nearly  25,000,000  pounds. 

Mining  explosives  are  divided  into  (i)  Low  Explosives, 
(2)  High  Explosives. 

Low  explosives,  examples  of  which  are  gunpowder  and 
Bobbinite,  may  be  fired  by  simple  ignition  and  do  not  re- 
quire detonation. 


FIG.  89. — Low  tension  detonator. 

High  explosives,  which  consist  of  an  explosive  compound, 
sometimes  alone  and  sometimes  mixed  with  other  substances, 
can  only  be  fired  with  a  detonator. 

Detonators  are  copper  cylinders  containing  a>  mixture  of 
fulminate  of  mercury  and  potassium  chlorate.  They  are 
made  in  various  sizes  and  strengths.  They  may  be  fired  by 
means  of  a  fuse  or  electrically.  In  fiery  mines  the  electrical 
method  must  be  used.  Electrically  fired  detonators  may 
be  (a)  Low  Tension  or  (b)  High  Tension  detonators. 

In  the  former  (Fig.  89)  a  current  of  low  voltage  but 
fairly  large  amperage  is  used. 


FIG.  90. — High  tension  detonator. 

The  wires  inside  the  detonator  are  connected  by  a  bridge 
of  platinum  wire  which  is  placed  in  position  in  the  priming 
composition  of  the  detonator.  The  free  ends  of  the  wires 
may  be  attached,  by  means  of  a  cable,  to  an  electric  battery 
or  small  portable  dynamo  worked  by  hand,  and  on  the 
current  being  applied  the  platinum  bridge,  being  a  bad  con- 
ductor of  electricity,  gets  sufficiently  hot  to  ignite  the 
priming  composition — an  easily  ignited  mixture — which 


1 88          An  Introduction  to  Mining  Science. 

in  its  turn  fires  the  fulminate  of  mercury.  The  resistance 
offered  by  the  copper  casing  of  the  detonator  causes  a  severe 
shock  or  concussion  which  is  communicated  to  the  explosive 
and  helps  in  its  decomposition. 

In  the  latter  (Fig.  90)  a  current  of  high  voltage  but  small 
amperage  is  employed,  and  the  priming  composition  is 
ignited  by  a  spark  passing  across  the  gap  left  at  the  inner 
end  of  the  wires. 

Detonators,  although  small,  contain  sufficient  explosive  to 
shatter  a  man's  hand,  and  as  fulminate  of  mercury  is  rather 
unstable,  they  should  be  handled  very  carefully  and  on  no 
account  be  played  with,  or  pulled  to  pieces.  A  number  of 

deplorable  accidents  have  happened  from  this  cause. 

i 

Permitted  Explosives, 

It  is  required  by  the  Coal  Mines  Act  that  in  mines  where 
gas  has  been  found  within  the  previous  three  months  in 
such  quantities  as  to  be  indicative  of  danger,  and  in  mines 
which  are  dry  and  dusty,  only  explosives  which  have  passed 
certain  official  tests  shall  be  used. 

These  tests  are  now  carried  out  at  Rotherham,  Yorkshire, 
and  are  briefly  as  follows  : — 

Charges  of  explosive  are  placed  in  a  steel  cannon  and 
fired  into  a  gallery  containing  an  explosive  mixture  of  air 
and  gas,  no  stemming  being  used. 

The  cartridges  do  not  fit  the  bore  of  the  gun  accurately 
but  have  an  air  space  of  more  than  f  inch  at  the  top. 

The  test  determines  the  maximum  charge  that  can  be 
fired  into  the  gallery  five  times  without  causing  an  ignition. 

In  addition  to  the  above,  a  test  in  a  mixture  of  coal  dust 
and  air  is  employed. 

Method  of  Stemming  and  Firing  a  Shot, 

It  is  assumed  that  the  shot  is  to  be  fired  in  a  mine  where 
permitted  explosives  must  be  used. 

After  drilling  the  shot  hole,  which  must  be  of  a  given 
size  to  comply  with  the  Coal  Mines  Act,  the  requisite 
amount  of  explosive,  which  is  in  the  form  of  cartridges,  is 
pushed  into  the  hole  by  means  of  a  wood,  brass,  or  copper 


Substances  Containing  Fixed  Oxygen.         189 

rod  or  stemmer.     The  detonator  is  fixed  in  the  last  cartridge 
in  the  manner  shown  in  Fig.  91  and  in  Fig.  92. 


FIG.  91. — Showing  method  of  fixing  detonator  in  explosive. 

The  hole  is  then  carefully  stemmed  with  clay  or  some 
non-inflammable  substance,  the  operator  holding  the  deton- 
ator wires  taut  with  one  hand  and  pushing  in  the  stemming 
by  means  of  the  "  stemmer".  The  stemming  is.  at  first 
lightly  tapped  with  the  stemmer  and  with  increasing  force  as 
the  hole  becomes  filled. 


FIG.  92. — Showing  method  of  fixing  detonator  in  charge,  and  method 
of  attaching  cable  to  detonator  wires. 

The  detonator  wires  are  next  attached  to  a  long  cable 
which  in  turn  is  connected  to  the  electric  battery  or  ex- 
ploder and  the  shot  is  fired. 

Miss-fire. 

If  the  shot  should  miss-fire  the  detonator  wires  must 
be  disconnected  from  the  exploder  and  TEN  MINUTES 


190          An  Introduction  to  Mining  Science. 


allowed  to  elapse  before  approaching  the  shot.  The  cable 
may  then  be  examined  and  another  attempt  made  to  fire 
the  shot.  If  it  again  misses  fire  a  further  TEN  MINUTES'  wait 


FIG.  93. — Photograph  showing  method  of  attaching  the  cable  to  the 
battery  when  firing  a  shot. 

is  necessary,  after  which  a  hole  may  be  drilled  alongside  and 
parallel  to  the  one  containing  the  miss-fired  shot,  but  must 
not  be  less  than  1 2  inches  away  from  it. 

Accidents  Due  to  the  Use  of  Explosives. 

It  is  pointed  out  in  the  Second  Report  of  the  Royal  Com- 
mission on  Mines,  published  in  1909,  that  during  the  years 
1896  to  1907  there  were  thirty-five  explosions  attributed  to 
shot-firing,  causing  the  death  of  377  persons.  During  the 
same  period  308  persons  were  killed  by  accidents  with 
explosives.  In  1911,  38  persons  were  killed  and  503 
injured  by  accidents  with  explosives,  and  in  1913  the  totals 
were  35  killed  and  1324  injured. 


Substances  Containing  Fixed  Oxygen.         191 

An  analysis  of  these  accidents  leads  one  to  the  conclusion 
that  many  of  them  are  preventable  if  proper  care  is  exercised 
and  if  regulations  are  fulfilled. 

The  following  are  some  of  the  more  frequent  causes  of 
accident : — 

Firing  by  electricity  when  persons  are  at  the  shot-hole. 

Not  taking  proper  cover  or  refuge  when  firing  the  shot. 

Hang  fires  and  returning  too  soon  to  the  shot-hole, 
ramming  or  stemming  the  charge. 

Striking  uriexploded  charges  when  removing  debris. 

Playing  with  detonators. 

It  is  very  important  that  the  explosives  in  Coal  Mines 
Order l  should  be  carefully  studied  by  all  who  expect  to  be 
engaged  in  any  way  in  shot-firing  operations  or  to  have 
anything  to  do  with  the  handling  or  use  of  explosives  in  or 
about  mines. 

QUESTIONS. 

1.  Draw  up  a  list  of  the  substances  containing  fixed  oxygen  which 
have  been  used  in  connexion  with  the  experiments  of  this  book. 

2.  How  could   you  put  the  free  oxygen  of  the  air  into  bondage 
with  phosphorus  ? 

3.  What  is  meant  by  saying  that  an  explosive  burns  by  its  own 
oxygen?     Mention   a   substance  which   will    not  burn   by   its   own 
oxygen. 

4.  What  explosives  are  used  in  your  pit?     Is  there  any  danger 
to  the  safety  of  the  pit  as  a  whole  by  their  use  ? 

5.  Is  it  possible  for  gunpowder  to  burn  with  no  air  present  ?     Give 
reasons  for  your  answer. 

6.  What  is  meant  by  a  "  permitted  explosive  "  ?     Give  reasons  for 
the  use  of  explosives  in  mines. 

7.  Describe  the  following  blasting  processes  :  (i)  Placing  the  charge 
in  the  hole;  (2)  the  stemming  of  the  hole  ;  (3)  the  firing  of  the  charge; 
(4)  the  effect  of  the  firing  on  the  coal,  rock,  and  air. 

8.  When  shots  are  being  fired  what  precautions  should  be  taken 
by  the  firer  and  others  adjacent  to  him  ? 


Wyman  &  Co.,  price  2d. 


CHAPTER  XII. 
DIFFUSION,  OR  THE  MOVEMENT  OF  GAS  PARTICLES. 

IN  considering  diffusion  as  the  cause  of  the  mixing  of  gases, 
let  us  take  a  lesson  from  the  Tables  giving  the  composition 
of  air  and  of  coal  gas. 

At  whatever  place  the  air  is  collected  it  is  found  to  con- 
tain oxygen  and  nitrogen  in  the  proportions  stated  on  p.  37. 
These  proportions  do  not  vary  whether  the  air  is  deep  down 
in  a  mine  or  high  up  on  a  mountain.  Moreover,  the 
proportions  are  the  same  whether  we  deal  with  a  cubic  foot, 
a  cubic  inch  of  air,  or  any  other  amount. 

Now  an  oxygen  particle  is  heavier  than  a  nitrogen  particle 
by  one-seventh  of  the  weight  of  the  latter,  and  yet  these  two 
gases  are  always  mixed  in  the  same  proportions  in  air,  at  all 
heights  and  depths.  The  lesson  to  be  learnt  therefore  is 
that  given  time  gases  will  become  uniformly  mixed  despite 
any  difference  in  weight. 

Let  us  consider  coal  gas.  If  the  sample  whose 
analysis  is  shown  on  p.  155  had  been  taken  from  any  other 
part  of  the  town's  gasholder,  it  would  have  shown  the  gases 
mixed  together  in  the  same  amounts.  No  one  would  be 
prepared  to  say  that  every  cubic  foot  of  the  gas  as  it  leaves 
the  heated  retorts  containing  the  coal  from  which  it  is  made, 
has  the  composition  there  given,  but  whatever  its  com- 
position before  it  enters  the  gasholder,  when  there  it  all 
mixes  uniformly  together  and  so  becomes  of  the  same 
composition  throughout.  Many  of  the  gases  in  coal  gas  are 
of  different  densities,  but  you  do  not  find  the  heaviest  at  the 
bottom  of  the  gasholder  and  the  lightest  at  the  top.  If  this 
were  the  case  then  hydrogen,  being  the  lightest,  would  be 
altogether  at  the  top,  and  occupy  about  half  the  gasholder 

192 


Diffusion,  or  the  Movement  of  Gas  Particles.      193 

(see  percentage  composition  on  p.  155),  then  the  heavier  gas 
— marsh  gas — would  come  as  a  thick  layer,  the  other  still 
heavier  gases  would  be  as  layers  underneath.  If  the  fore- 
going were  true,  it  would  follow  that  when  the  top  gas  was 
drawn  off  it  would  have  no  lighting  power,  there  is  no  lumin- 
osity when  burning  marsh  gas  and  hydrogen.  Stirrers  would 
have  to  be  put  in  the  gasholders  to  mix  the  gases,  but  as 
gas  particles  are  capable  of  moving  and  roaming  they  mix 
themselves  together  uniformly.  The  gas  particles  do  not 
collect  together  in  crowds  of  their  own  kind,  but  all  varieties 
are  represented  and  in  the  same  proportion  however  big  or 
small  the  crowd  may  be.  They  arrange  themselves  in  the 
gasholder  so  that  every  cubic  inch  of  space  is  rilled  in  the 
same  proportions. 

Experience. 

Consider  a  stream  of  white  smoke,  issuing  slowly  from  a 
chimney  on  a  day  free  from  wind.  The  smoke,  and  the  gases 
mixed  with  it,  will  steadily  spread  in  the  surrounding  atmosphere, 
and  in  time  the  smoke  will  not  be  seen,  its  particles  have  spread 
uniformly  in  the  atmosphere  around  by  their  own  movements. 

A  black  cloud  of  smoke  would  behave  differently  ;  its  particles 
are  bigger  and  heavier  than  white  smoke  particles.  It  would  fall 
to  the  earth  almost  as  a  whole  ;  this  is  not  diffusion  but  falling 
by  weight. 

The  gases  which  come  out  with  the  smoke  in  either  case 
are  not  visible  and  their  particles  never  fall  to  the  ground 
but  mix  with  the  air.  This  mixing  will  go  on  long  after 
they  have  lost  the  rush  which  they  have  on  coming  out  of 
the  chimney.  It  goes  on  because  the  individual  particles 
never  lose  their  power  of  moving ;  ceaseless  movement  is 
a  part  of  their  natural  gifts.  This  ceaseless  movement, 
which  all  gas  particles  possess,  in  time  makes  them  spread 
out  in  the  air ;  they  cannot  long  remain  as  a  swarm  of  gas 
particles,  but  are  bound  to  distribute  themselves. 

Stagnant  Gas. 

It  should  be  thoroughly  realized  that  there  cannot  be 
such  a  thing  as  stagnant  gas,  even  the  heaviest  gas  we  have 
in  mines — carbon  dioxide — consists  of  moving  particles  and 
cannot  therefore  become  stagnant.  Its  heavy  particles 

13 


194 


Introduction  to  Mining   Science. 


move  slowly  away  from  the  bottom  of  disused  shafts  and 
wells.  Suffocation  has  been  caused  by  accumulations  de- 
spite this  slow  movement.  If  gas  appears  to  remain  in  a 
hole,  or  a  dead  end,  or  a  corner,  for  days  it  is  not  because  it  is 
stagnant,  the  gas  is  moving  —  diffusing  —  out  of  the  place  but 
gas  is  at  the  same  time  feeding  into  the  place,  hence  one  is 
liable  to  reason  wrongly  and  say  the  gas  is  stagnant.  Move- 
ment of  the  particles  goes  on  even  when  the  gas  accumulation 
is  not  affected  by  the  rush  of  the  ventilating  current,  and  also 
in  places  where  the  current  has  become  extremely  weak. 
That  part  of  the  gas  which  has  diffused  out  into  a  ventilating 
current  is  swept  along  by,  and  with  it,  its  particles  still 
have  a  motion  of  their  own,  but  the  current  sweeps  them 
along  by  its  superior  force. 

Illustration. 

Any  place,  e.g.  train,  tram,  hotel,  may  be  filled  right 
throughout  the  day,  but  no  one  would  assume  that  the  same 
people  have  occupied  it  all  the  time.  People  have  entered  and 

departed  and  thus  the  supply  has  been  kept  up. 

It  is  the  same  with  gas  particles   in  any  space 

other  than  a  gas-tight  one. 

Liquids,  other  than  oils,  mix  amongst  each 
other  very  slowly,  but  on  account  of  many 
liquids  being  coloured,  they  afford  an  experi- 
mental way  of  showing  to  the  eye  that  mixing 
does  take  place.  The  majority  of  gases  are 
colourless,  and  so  it  is  not  as  easy  to  show  that 
they  diffuse  amongst  one  another. 

Experiment, 

Half  fill  a  gas  cylinder  with  water,  and  then 
pour  gently  a  thin  layer  of  oil  on  its  surface.  Leave 
the  liquids  for  any  length  of  time  and  they  will 
remain  as  two  unmixed  columns  (see  Fig.  94). 

Repeat  the  experiment,  but  instead  of  using 
a  jayer  of  oji  pOur  gently  a  layer  of  coloured 
methylated  spirit  —  coloured  by  a  drop  of  ink  —  on  to  the  water 
surface.  Make  a  mark  on  the  cylinder  where  the  two  columns 
meet.  Leave  the  apparatus  and  notice  the  change  which  goes 
on  at  the  two  surfaces  in  contact. 


FIG.  94.—  Li- 
quid  float- 
ing  on 
water. 


Diffusion^  or  the  Movement  of  Gas  Particles.      195 

Mineral,  animal,  and  vegetable  oils  will  not  mix  by  their 
own  movement  with  water.  Despite  the  fact  that  the 
particles  of  water  and  oil  are  moving  slowly,  each  remains  with 
its  own  kind  of  particle  ;  they  will  not,  or  cannot,  diffuse. 

In  the  case  of  water  and  methylated  spirit,  their  particles 
will  move  into  each  other's  territory,  i.e.  diffusion  will  take 
place,  as  is  evidenced  by  the  alteration  of  colour  at  the  two 
surfaces  in  contact. 

The  advantage  which  a  liquid  possesses  in  being  coloured 
is  something  like  the  advantages  a  gas  possesses  in  having 
an  odour.  The  first  one  helps  by  appealing  to  the  eye  and 
the  second  one  by  appealing  to  the  nose.  When  a  puff  of 
any  gas,  be  it  coal  gas  or  fire-damp,  passes  into  the  air  the 
swarm  of  particles  making  up  the  puff  soon  begin  to  move 
apart  from  one  another  and  so  spread  out  in  all  directions, 
and  whether  it  be  a  hall,  a  bedroom,  or  a  mine,  they  will  in 
time  be  present  in  every  part  of  it ;  unless  sucked  out  by  a 
ventilating  current, 

A  Comparison, 

If  two  solids  are  placed  in  contact  their  particles  will  not 
mix  by  their  own  action.  Liquid  particles  will  mix  slowly  by 
their  own  movement,  with  a  few  exceptions,  chiefly  oils.  Gas 
particles  mix  by  their  powers  of  movement  and  there  are  no 
exceptions. 

The  diffusion  of  gas  particles  through  walls  which  are 
apparently  gas-tight  shows  their  extreme  smallness.  Walls 
of  brick  or  stone  are  not  easily  made  air-tight. 

Experiment, 

Fit  up  a  porous  pot  with  a  well-fitting  stopper  through  which 
projects  a  glass  tube.  Attach  to  the  tube  by  a  piece  of  rubber 
a  U-tube  containing  some  coloured  water  in  the  bend,  and  lower 
the  porous  pot  into  a  jar  of  carbon  dioxide  (see  Fig.  96),  or  up 
into  an  inverted  jar  of  hydrogen  or  coal  gas  (see  Fig.  95).  Notice 
if  the  level  of  the  water  in  the  U-tube  is  slowly  altered. 

The  U-tube  used  may  be  a  smaller  one  than  those  shown  in 
the  figures  ;  the  one  made  for  experiment  on  p.  49  will  do. 

The  following  actions  go  on  during  the  experiment : 
particles  of  gas  in  the  jars  are  passing  inwards  through 

13  * 


196          An  Introduction  to  Mining  Science. 

the  pores  of  the  pot  and  particles  of  air  are  passing  out- 
wards through  the  pot.  In  the  experiment  of  Fig.  95  more 
hydrogen  or  coal  gas  particles  get  in  than  air  particles  get 
out ;  therefore  overcrowding  goes  on  in  the  U-tube,  and  the 


FIG.  95. — Showing  the  method          FIG.  96. — Showing  the  method 
with  hydrogen  or  coal  gas.  with  carbon  dioxide. 

U-tube  on  stand.  U-tube  without  stand. 

water  moves  down  the  left  arm  to  accommodate  the  extra 
particles.  In  the  case  of  carbon  dioxide  the  water  will  rise 
in  the  left  arm  of  the  tube  owing  to  more  air  particles  getting 
out  than  carbon  dioxide  particles  are  getting  into  the  tube. 

Experiments, 

1 .  A  bottle  or  gas  cylinder  filled  with  any  one  of  the  following 
gases,  (a)  coal  gas,  (b}  carbonic   acid,  (c)   hydrogen,    may  be 
shown  to  have  lost  its  contained  gas  after  a  lapse  of  time  by  the 
use  of  a  lighted  taper.     Keep  (a)  and  (c)  inverted. 

2.  If  any  of  the  three  gases  mentioned  is  shut  up  in  a  porous 
pot  by  a  rubber  stopper,  then  opened  later   and   tested   by   a 
lighted  taper,  it  will  be  found  to  have  disappeared. 

3.  Place  a  beaker  on  a  scale  pan  and  balance  it  when  filled  with 
carbonic  acid  gas  (Fig.  13,  p.  34).     The  beaker  should  be  dry 
and  no  liquid  allowed  to  fall  in  from  the  carbon  dioxide  apparatus 
tube.     Notice  the  alteration  in  the  balance  after  the  lapse  of  a 
few  minutes. 


Diffusion^  or  the  Movement  of  Gas  Particles.      197 

The  gases  hydrogen  and  coal  gas  are  lighter  than  air, 
and  so  the  air  tends  to  fall  into  any  vessel  containing  them 
and  force  them  out.  In  order  therefore  to  show  that  diffusion 
goes  on  the  cylinders  must  be  held  upside  down.  In  these 
circumstances  the  air  tends  to  shut  the  gas  in  the  cylinder, 
but  cannot  on  account  of  its  particles  possessing  move- 
ment. 

With  carbon  dioxide,  as  it  is  heavier  than  air,  the 
vessel  must  be  kept  upright ;  otherwise  if  turned  upside, 
down  it  would  fall  out  as  a  whole.  By  preventing  falling  out 
getting  out  individually,  by  diffusion,  can  be  proved. 

The  explanation  of  the  action  in  Expt.  2,  p.  196,  is  based 
upon  the  fact  that  you  cannot  shut  up  a  gas  unless  it  be 
in  a  special  gas-tight  vessel.  A  gas  will  get  through  a 
porous  vessel ;  only  by  glazing  it  or  filling  up  its  pores  could 
it  be  made  gas-tight. 

Experiment. 

Take  two  gas  cylinders  which  fit  well  when  their  mouths  are 
in  contact,  one  cylinder  being  above  the  other.  Calling  L  the 
lower  and  U  the  upper  cylinder,  fill  L  with  air  and  U  with  coal  gas. 
Put  them  one  above  the  other  and  apply  a  light  in  5  minutes. 
Repeat  experiment  with  the  cylinder  containing  coal  gas  below 
the  cylinder  containing  air. 

When  the  air  is  under  the  coal  gas,  then  any  mixing 
which  has  taken  place  is  due  to  true  diffusion — the  mixing 
which  has  occurred  by  the  particles'  own  unaided  movement 
is  diffusion.  In  the  case  of  the  air  being  above,  it  would 
tend,  by  its  greater  weight,  to  mix  with  the  underlying  coal 
gas,  and  such  action  is  not  true  diffusion.  Pulling  a  particle 
down  is  different  from  the  particle  moving  down  by  its 
own  action  ;  it  is  weight  that  does  the  pulling  down,  and 
does  it  quickly,  whereas  the  particle's  roving  power  is  a  slow 
movement. 

The  particle  by  its  own  movement  may  move  up  and 
down,  but  weight  never  pulls  up  a  thing  after  pulling  it 
down. 


198  An  Introduction  to  Mining  Science. 

SPEED  OF  DIFFUSION  AND    HEAVINESS  OF  GAS 
PARTICLES. 

Gas.                                            Relative  Relative 

speeds.  heaviness. 

Hydrogen          ...          3*8  i 

Marsh  gas         ...          1-3  8 

Air          .            .          .          .          i'o  I4-J 

Carbon  dioxide          .                     '8  22 

It  will  therefore  be  seen  from  the  second  and  third  columns 
that  the  heavier  a  gas  particle  is  the  slower  it  diffuses. 

Experience, 

You  have  no  doubt  noticed  that  a  flower-pot  shows  moisture 
on  the  outside  when  a  plant  in  it  is  kept  well  watered.  The  water 
particles  pass  through  the  pores — fine  tubes — of  the  pot.  If  the 
pot  is  kept  in  a  saucer  of  water  the  water  will  rise  in  the  material 
of  the  pot  as  well  as  in  the  soil. 

Ask  yourself  why  tea-cups  are  glazed,  and  why  badly  glazed 
jam-pots  or  fancy  flower-pots  are  not  quite  watertight. 

Just  as  water  particles  pass  through  the  pores  of  an  un- 
glazed  vessel,  so  will  air  particles  get  through  bricks  and 
keep  gob  fires  on  the  smoulder.  The  smell  of  cooking  is  not 
an  easy  thing  to  confine  to  its  proper  room  in  a  house  or 
hotel,  the  particles  which  smell  overcome  all  obstacles  to 
diffusion. 

The  experiments  also  point  out  how  difficult  it  is  to  shut 
up  a  gas ;  brick  walls  enclosing  a  waste  heap  may  let  out 
some  gas,  and  let  in  some  air,  on  account  of  the  porosity  of 
ordinary  bricks. 

The  teaching  of  the  experiments  in  this  chapter  is  of  great 
importance  to  those  engaged  in  mining.  In  mines  there  are 
many  sources  of  different  gases,  some  of  which  are  inflam- 
mable and  therefore  dangerous  from  an  explosive  standpoint, 
others  non-inflammable  but  dangerous  from  a  health  point 
of  view.  One  cannot  help  but  regard  the  mine  as  a  big 
mole  run  deep  down  in  the('earth  with  two  borings  or  shafts,  one 
for  taking  in  air  and  the"other  for  clearing  out  the  air  after 
mixing  with  mine  gases.  Thus  the  ventilation  current  helps 
to  sweep  out  all  gases,  but  at  the  same  time  it  is  diffusion  which 


Diffusion,  or  the  Movement  of  Gas  Particles.      199 

helps  to  equalize  the  composition  of  the  air  of  the  workings. 
Whether  it  be  carbon  dioxide  given  out  by  men  and  animals 
breathing,  inflammable  gas  given  out  by  blowers,  or  from 
the  face  of  the  coal  or  from  roof,  all  are  mixing  with  the 
air  of  the  ventilating  current.  In  this  way  all  objection- 
able gases  get  diluted ;  they  do  not  accumulate  around  the 
place  or  man  which  are  their  sources,  and  so  this  natural 
action  of  diffusion  promotes  health  and  safety.  As  soon  as 
fire-damp  has  diffused  into  sufficient  air  to  reduce  it  to  less 
than  5-^  per  cent,  there  is  no  fear  of  an  explosion  :  see  figures, 
p.  107. 

QUESTIONS. 

1.  A  gas  tap  accidentally  left  open  in  the  kitchen  was  detected  by 
an  occupant  of  the  attic.     Explain  how  this  was  possible. 

2.  A  motor-car  passing  down  a  street  left  an  objectionable  odour 
behind  which  finally  disappeared.      Explain  how  it  was  lost  to  the 
sense  of  smell. 

3.  A  swarm  of  bees  leave  a  hive  and  spread  over  the  surrounding 
country,  but  return  again  one  by  one  at  night.     What  part  of  this 
action  is  similar  to  the  diffusion  of  gas  particles  ? 

4.  A  cup  of  tea  has  a  small  amount  of  milk  poured  into  it  and  then 
left  for  a  considerable  time.     Can  you  explain  why  it  finally  has  a  uni- 
form appearance  ? 

5.  The  amounts  of  carbon  dioxide  and  marsh  gas  in  the  return  air  of 
a  mine  was  •!  and  '75  per  cent  respectively.     Do  you  think  these  per- 
centages would  be  the  same  near  the  source  of  the  gases  ? 

6.  In  a  manufacturing  town  on  a  windless  day  large  volumes  of 
smoke  were  seen  passing  into  the  air,  but  later  on  the  air  had  cleared. 
What  might  have  happened  to  the  smoke  ? 

7.  What  do  you  mean  by  the  word  diffusion  ?     If  a  gas  had  no 
power  of  movement  could  a  leakage  find  its  way  all  over  a  house  ? 

8.  What  processes  going  on  in  Nature  help  to  make  air  uniform 
after  its  being  fouled  in  several  ways  ? 

9.  Bricks   are   of  two  kinds — with    and  without   a    glazed   face. 
Through  which  do  you  think  a  gas  or  a  liquid  is  the  more  likely  to 
pass  ? 

10.  In  a  public  hall  smoking  is  permitted  on  the  ground  floor  only, 
but  in  the  balconies  it  is  noticed  that  the  air  is  uniformly  hazy  with 
smoke.     Explain  how  this  uniformity  is  brought  about. 

11.  Use  the  facts  of  the  foregoing  question  to  define  the  follow- 
ing :  (i)  uniform  density ;  (2)  varying  density ;  (3)  the  movement  of 
particles. 


CHAPTER  XIII. 
SUBSTANCES  AND  THEIR  CHANGES. 

THE  substances  which  make  up  this  world  may  be  divided 
into  two  groups ;  those  which  attack  one  another  at  once 
when  they  come  together,  and  those  which  require  heating 
to  start  an  attack  upon  one  another. 

1.  Substances   which    with  no   previous  heating   attack 
one  another  when  they  come  together,  and  after  the  attack 
hold  one  another  in  bondage  : — 

Iron,  oxygen,  and  water,  as  in  rust. 

Mortar  and  carbonic  acid,  as  in  its  hardening. 

Gob  waste  and  oxygen. 

2.  Substances   which  when  slightly  heated  are  attacked 
by  oxygen,  and  after  the  attack  hold  the  oxygen  in  bon- 
dage with  their  constituents  :— 

Coal  gas.     Coal  dust.     Petroleum. 

Let  us  consider  first  a  few  well-known  substances  which 
attack  one  another  without  any  heating  and  produce  a  new 
substance  as  a  result  of  the  action. 

Experience. 

Iron  exposed  to  the  air  undergoes  a  change  which  is  called 
rusting ;  the  substance  produced  by  the  action  is  called  "rust". 

The  new  thing  produced,  rust,  should  receive  attention 
because  it  differs  very  much  from  the  substances  of  which  it  is 
made.  Let  us  tabulate  some  of  these  differences  under  their 
respective  heads : — 

Iron.               Oxygen.         Moisture.  Rust. 

Grey.                 Colourless.          Colourless.  Reddish-brown. 

Tough  solid.                 Gas.                  Vapour.  Friable  solid. 

Air  attacks  it.  Air  no  action  on  it. 

200 


Substances  and  their  Changes.  20 1 

What  is  it  in  the  air  that  attacks  the  iron  ?  Moisture  we 
know  is  always  present,  and  this,  along  with  the  oxygen, 
set  up  the  attack.  The  iron  is  solid  and  gives  us  the  im- 
pression that  it  is  passive  in  the  action,  but  such  is  not  the 
case.  In  all  changes  which  produce  a  new  substance,  the 
particles  of  each  substance  are  joining  in  the  attack,  but 
not  necessarily  all  with  the  same  vigour. 

Rust  then  differs  fundamentally  from  its  constituents.  It 
is  necessary  to  emphasize  the  fact  that  the  new  substance 
consists  of  all  the  three  things  concerned  in  the  action : 
iron,  oxygen,  and  moisture.  If  we  look  at  rust  it  certainly 
does  not  suggest  there  is  moisture  in  it,  it  is  quite  dry.  It 
is  one  of  the  most  difficult  things  to  realize  that  when  sub- 
stances attack  one  another  they  become  fixed  or  united 
together,  and  each  one  loses  its  own  individual  characteristics, 
and  their  union  is  so  strong  that  it  is  difficult  to  break  them 
again  apart.  Particular  attention  should  be  paid  to  the 
idea  of  the  substances  becoming  fixed  or  united  together, 
it  is  quite  distinct  and  different  from  the  idea  of  being  mixed 
together.  Nature  takes  the  iron,  oxygen,  and  moisture, 
unites  them  together,  and  the  new  substance,  rust,  is  not  only 
different  to  look  at  but  seems  fundamentally  different  from 
the  original  materials. 

"  There  are  agents  in  Nature  able  to  make  the  particles  of  a  body 
stick  together  by  very  strong  attraction." — SIR  ISAAC  NEWTON. 

Analogy  and  Experiment  will  help  an  Explanation, 

Old  iron  structures  such  as  fire-grates,  fly-wheels,  grates, 
broken  cast-iron  pipes,  baths,  kitchen  boilers,  iron  window 
frames,  etc.,  are  collected  by  the  old  iron  merchant  and 
sent  where  iron  is  smelted.  They  all  go  into  the  melting 
pot  and  lose  their  individuality,  and  as  things  they  could 
not  be  recognized  in  any  new  structure  made  from  them. 

The  particles  of  iron  in  the  old  structures  are  loosened 
from  one  another  by  the  heat  applied,  and  the  solid  becomes 
a  liquid.  The  particles  of  solid  iron  are  said  to  be  held 
together  by  the  force  of  cohesion,  of  which  there  is  very  little 
in  the  liquid  state.  Heat  therefore  seems  to  overcome  this 
force,  and  as  the  liquid  iron  loses  its  heat  and  again  becomes 
solid  the  force  of  cohesion  again  acts ;  it  should  be  noticed 


2O2  An  Introduction  to  Mining  Science. 

that  heat  is  capable  of  overcoming  a  force  which  holds 
particles  together.  Suppose  this  old  iron  had  got  mixed 
with  some  sulphur,  popularly  known  as  brimstone,  and 
the  two  things  had  got  melted  together.  On  cooling  there 
would  not  be  a  lump  of  iron  and  a  lump  of  sulphur  to  be 
seen,  but  a  new  substance  quite  unlike  the  sulphur  and  the 
iron  from  which  it  was  made. 

Experiment. 

Mix  well  together  equal  weights  of  iron  filings  and  flowers  of 
sulphur.  Notice  that  no  change  goes  on,  but  that  the  two  con- 
stituents can  be  seen  lying  side  by  side.  If  you  have  a  magnet 
separate  the  iron  filings  from  a  part  of  the  mixture,  and  notice 
that  no  change  has  occurred  to  the  filings  or  to  the  sulphur. 

The  magnet  passing  through  the  mixture  withdraws  the 
iron  and  leaves  the  sulphur. 

Continuation  of  the  Experiment. 

Place  some  of  the  mixture  in  a  test  tube,  say  a  layer  of  | 
inch.  Heat  it  in  the  Bunsen  flame  gently  (see  Fig.  97),  and 
carefully  notice  any  action  that  happens. 

The  sulphur  melts  and  darkens  and  then  a  bright  red 
glow  passes  through  the  mixture.  When  the  glow  starts  re- 
move the  tube  from  the  flame  and  notice  that  it  does  not 
cease,  it  goes  on  without  any  outside  heat.  This  fact  is  of 
great  importance.  The  outside  heat  is  used  in  melting  the 
sulphur,  i.e.  overcoming  the  cohesion  of  its  particles,  and 
in  heating  up  the  iron  and  sulphur  to  the  temperature  re- 
quired for  their  attacking  each  other.  As  soon  as  the  red 
glow  appears  it  means  that  the  iron  and  sulphur  particles 
are  attacking  each  other,  and  in  the  attack  sufficient  heat 
is  made  to  produce  a  red  heat.  Whilst  this  glow  is  pro- 
ceeding the  iron  and  sulphur  are  losing  their  individual 
existence,  they  are  becoming  locked  together  by  a  force, 
called  chemical  force,  and  the  glow  is  a  proof  it  is  acting 
vigorously. 

Conclusion  of  the  Experiment. 

Break  the  tube  and  look  at  the  cooled  substance,  it  is  very 
much  unlike  sulphur,  harder  than  it,  but  less  hard  than  iron.  It 


Substances  and  their  Changes.  203 

is  bluish-grey  in  colour,  and  a  magnet  has  no  action  on  it  even  if 
the  substance  is  powdered.  Notice  it  has  a  uniform  appearance 
which  the  original  mixture  had  not.  Is  it  like  the  original  com- 
ponents ? 

A  new  substance  has  been  formed  and  its  name,  iron 
sulphide,  suggests  its  components  which  as  free  individual 
substances  have  disappeared. 


FIG.  97. — Heating  the  mixture  in  a  test  tube  so  as  to  bring  about  a 
change. 

Here,  as  in  the  formation  of  other  new  substances,  there 
has  been  an  attack  by  the  particles  on  each  other,  producing 
the  fire  of  the  action,  and  the  particles  of  the  two  original 
substances  have  become  held  together  by  chemical  force, 
a  force  much  stronger  than  cohesion.  When  chemical 
force  is  acting  between  substances  heat  is  being  produced ; 
on  the  other  hand,  heat  acting  on  substances  may  be  over- 
coming chemical  force.  One  iron  particle  locks  itself  to  one 
sulphur  particle,  and  if  in  the  experiment  an  excess  of  one 
substance  is  left  in  the  tube  it  shows  we  have  not  been 


204          An  Introduction  to  Mining  Science. 

skilled  enough  to  obtain  an  equal  number  of  particles  of 
sulphur  and  iron. 

If  we  had  weighed  out  if  times  more  iron  than  sulphur 
this  condition  of  equal  number  of  iron  and  sulphur  particles 
would  have  been  realized. 

In  all  these  actions  between  bodies  it  is  really  a  case  of 
the  particles  attacking  one  another.  In  the  case  of  rust 
formed  in  the  air  two  particles  of  iron  are  attacked  by  three 
of  oxygen  and  three  of  water,  and  after  the  attack  they  all 
continued  to  hold  together  as  a  family  of  particles,  i.e.  as  a 
compound  particle. 

The  holding  together  of  the  particles  is  not  an  easy 
thing  to  grasp,  because  it  is  not  a  holding  together  by  hooks, 
screws,  nails,  or  cement,  but  the  following  illustration  may 
help. 

To  break  a  piece  of  steel  a  square  inch  in  section  would  re- 
quire a  pull  of  30  tons.  This  then  is  the  force  required  to  tear 
apart  the  particles  of  the  steel ;  there  must  be  many  particles 
in  the  two  separated  faces  and  their  united  holding  power 
equals  30  tons.  This  force  is  sometimes  spoken  of  as  the 
cohesion  of  the  particles ;  it  is  strongest  in  solids,  in  its 
absence  the  solid  would  crumble  to  powder.  Compare 
rust  with  steel,  these  two  substances  show  that  cohesion 
differs  in  different  substances.  There  is  little  cohesion  in 
rust,  yet  its  constituent  particles  of  iron,  moisture,  and  oxygen 
hold  firmly  together.  This  force  holding  particles  of  a 
different  nature  together  is  called  chemical  force,  or  attrac- 
tion; it  wants  distinguishing  from  cohesion,  for  the  latter 
may  be  overcome  by  pulling  at  a  thing  until  it  breaks, 
whereas  chemical  force  cannot  be  overcome  in  that  way. 

Ice,  Water,  and  Steam, 

These  three  substances  are  actually  three  different  condi- 
tions of  one  substance,  and  if  their  changes  into  one  another 
were  less  well  known  to  us  it  is  possible  we  might  believe 
them  to  be  different  substances. 

There  are  well-defined  differences  in  them  ;  one  is  a  solid, 
easily  broken  and  capable  of  being  moulded ;  the  other  is 
a  liquid  of  a  light  blue  colour,  and  dissolves  many  things ;  the 


Substances  and  their  Changes.  205 

last  is  a  vapour  that  is  quite  invisible.  Why  should  the  same 
thing  appear  in  three  different  states? 

The  differences  may  be  connected  with  the  amounts  of  heat 
in  them,  for  we  all  know  there  is  more  heat  in  steam  than  in 
water  or  ice.  Such  a  fact  suggests  that  when  heat  is  run  off 
a  body,  or  put  into  a  body,  its  properties  change.  This  is 
a  very  important  fact,  and  so  we  may  regard  the  changes  in 
a  substance  to  be  influenced  by  losing  or  gaining  heat. 

The  differences  may  be  influenced  by  the  varying  distances 
between  the  particles  and  by  the  size  of  them. 

The  distance  between  the  particles  of  steam  must  be 
greater  than  between  the  particles  of  water  or  ice,  inasmuch 
as  steam  occupies  1650  times  more  space  than  the  water 
from  which  it  is  made. 

We  may  picture  each  steam  particle  as  free  from  any  or 
all  other  steam  particles,  but  as  steam  passes  to  water  three 
or  four  particles  may  unite  together  and  remain  united  as 
long  as  they  are  water,  and  in  becoming  ice  there  may  be  a 
further  locking  together  of  particles.  This  union  of  particles 
along  with  a  giving  up  of  heat  may  be  entirely  responsible  for 
the  different  properties  of  the  three  substances.  It  is  quite 
true  that  when  particles  become  associated  together,  or  driven 
apart,  there  is  always  a  change  in  the  properties  of  the  sub- 
stance. It  is  known  that  the  particles  of  water  are  made 
up  of  groups  of  steam  particles,  i.e.  that  two,  three,  or  four 
particles  group  themselves  together  when  steam  changes  to 
water  and  remain  grouped  together. 

It  is  now  necessary  to  go  a  step  further  in  this  idea  of  the 
properties  of  a  substance  depending  on  the  number  of  par- 
ticles holding  together  as  a  group.  Is  a  particle  of  water, 
steam,  or  ice,  a  simple  thing,  i.e.  is  it  made  of  still  smaller 
particles?  Are  there  smaller  particles  making  up  a  par- 
ticle of  water  and  are  they  alike  or  unlike  ? 

Supposing  some  steam  particles  were  heated  to  a  very 
high  temperature  each  steam  particle  would  break  up  into 
one  oxygen  and  two  hydrogen  particles,  the  latter  still 
united  together.  Here  then  heat  simplifies  the  steam  par- 
ticle and  resolves  it  into  its  simple  and  final  constituent 
particles.  These  particles  are  quite  different  from  steam 
particles  ;  oxygen  will  burn  up  most  things,  hydrogen  will 


206         An  Introduction  to  Mining  Science. 

easily  burn  with  flame,  whereas  steam  can  do  neither  ;  on  the 
other  hand,  it  will  stop  a  body  burning.  It  is  therefore  impor- 
tant to  remember  that  when  simple  or  dissimilar  particles 
group  themselves  together,  heat  is  concerned  in  the  group- 
ing, and  the  grouped  particles  have  different  properties  from 
the  ungrouped  particles. 

All  the  substances  of  this  world  consist  of  particles.  Some 
very  active,  restless  particles,  e.g.  oxygen,  are  always  attacking 
other  particles,  and  in  this  way  changes  are  always  taking 
place.  In  these  changes  heat  is  in  some  way  concerned  ; 
when  oxygen  is  an  attacking  agent  heat  is  always  produced. 
This  is  even  the  case  in  rusting,  but  as  the  action  goes  on 
slowly  the  heat  is  produced  in  very  small  quantities. 

When  a  little  heat  has  to  be  supplied  to  start  an  action  there 
is  always  as  the  action  goes  on  some  more  produced.  In 
lighting  the  gas  or  the  fire  very  little  heat  is  required  to 
start  the  action,  and  after  this  all  the  heat  produced  is  due 
to  the  attack  of  the  oxygen  of  the  air  upon  the  gas  or  coal. 

In  this  attack  by  oxygen  particles  upon  the  particles 
making  up  gas  and  coal,  new  substances  are  produced,  due 
to  new  grouping  of  the  particles  taking  part  in  the  action. 
This  production  of  new  substances  is  evidenced  by  the  loss 
of  smell  by  the  gas  and  in  the  case  of  the  coal  by  the  sub- 
stances which  go  up  the  chimney,  and  the  ashes  left  in  the 
grate.  The  size  of  the  particles  of  substances  and  the  changes 
they  undergo  from  visibility  to  invisibility  is  expressed  in 
Tennyson's  lines : — 

The  million  millionth  of  a  grain 

That,  ever  vanishing,  never  vanishes. 

The  Militancy  of  Oxygen. 

Oxygen  particles  are  very  energetic,  and  either  feebly  or 
strongly  they  will  attack  most  things.  This  attack  in  many 
cases  goes  on  at  the  ordinary  daily  temperature.  In  other 
cases,  the  oxygen  particles  require  a  start,  which  means  the 
substances  must  be  warmed  or  heated  for  it  to  carry 
on  its  actions.  In  either  case  the  oxygen  comes  to  the  end 
of  its  attack  and  then  it  is  a  prisoner — held  by  the  force  of 
chemical  attraction — in  the  hands  of  the  substance  it  at- 
tacked. 


Substances  and  their  Changes.  207 

Oxygen  attacks  at  the  ordinary  temperature  : — 

The  metals  iron,  sodium,  and  potassium. 
Phosphorus. 
Very  dry  coal  dust. 
Substances  found  in  the  gob. 

At  a  higher  temperature  it  attacks  most  things,  e.g.  wood, 
gas,  coal,  illuminating  oils,  etc. 

Some  substances  have  long  been  conquered  by  the  oxygen 
as  fully  as  possible  and  the  attack  is  finished ;  sand,  water, 
rust,  carbon  dioxide,  represent  substances  which  are  no 
longer  open  to  further  attack  by  oxygen.  Whatever  there 
is  in  these  substances  besides  oxygen  it  has  been  attacked, 
and  come  to  its  limit  as  regards  taking  up  oxygen. 

Oxygen  is  the  carrier  of  the  fiery  cross,  and  if  it  gets  an 
opportunity  with  those  bodies  we  call  combustible  there  is 
soon  flame  and  heat.  It  can  attack  all  substances  contain- 
ing carbon  and  so  produces  carbon  dioxide  gas,  the  great 
food  of  plants.  Our  blood  and  bodies  are  a  prey  to  oxygen, 
so  in  time  we  become  plant  food. 

It  is  the  ease  with  which  many  substances  are  open  to 
attack  by  others  that  there  is  danger  in  the  mine. 

Substances  Made  of  One  Kind  of  Material. 

The  scientific  man  will  tell  us  that  out  of  eighty  simple 
substances  all  the  various  materials  of  this  world  are  made, 
and  by  a  simple  substance  is  meant  one  made  only  of  one 
kind  of  particle.  No  one  has  ever  succeeded  in  breaking 
up  any  one  of  these  simple  substances  into  two  different 
substances,  or  of  getting  out  of  it  anything  other  than  it- 
self. These  simple  substances  are  called  Elements  ;  several 
are  gases,  few  are  liquids,  and  many  are  solids.  A  list  of  the 
commoner  ones  is  given  here : — 

Gases.  Metals.  Not  Metals. 

Oxygen.  Iron.  Tin.  Carbon. 

Nitrogen.          Copper.        Silver.  Sulphur. 

Hydrogen.        Zinc.  Gold.  Phosphorus. 

Lead.  Mercury. 

The  thousands  of  substances  in  this  world  which  are  not 


208         An  Introduction  to  Mining  Science. 

simple  are  all  made  up  of  two  or  more  of  these  eighty  simple 
substances.  These  eighty  elements  are  the  foundation  of 
all  substances,  and  it  is  by  their  particles  joining  and  holding 
together  in  different  numbers  and  different  ways  that  we  have 
countless  different  substances.  Nature  works  something 
like  a  builder  does,  each  has  things  with  which  to  work. 
Nature  has  elements,  a  builder  has  bricks,  and  just  as  the 
builder  may  fix  his  bricks  to  produce  different  structures 
from  a  simple  brick  wall  to  a  complicated  palace,  so  Nature 
fixes  the  particles  of  her  elements,  two  or  more  together,  to 
produce  a  simple  thing  like  water  or  a  complicated  thing 
like  coal. 

It  may  be  difficult  to  realize  that  when  particles  are  joined 
together  by  chemical  force  there  should  be  so  great  a  change 
in  their  properties.  Let  us  consider  a  few  well-known  and 
striking  changes.  The  plant  in  all  its  parts — and  the  flower 
is  often  a  very  beautiful  part  of  it — is  made  up  of  materials 
which  it  draws  from  air  and  soil  alone.  These  materials 
are  the  raw  materials  of  the  plant,  and  by  chemical  force 
acting  on  the  particles  of  these  materials,  rearranging  them 
in  different  ways,  it  produces  all  the  glory  of  the  plant. 
Science  says  that  this  great  alteration  is  due  to  a  new 
arrangement  of  the  particles,  which  in  their  original  state 
formed  part  of  the  invisible  air  or  a  part  of  that  uninterest- 
ing, and  not  very  beautiful,  substance  called  the  soil.  Chemi- 
cal force  is  therefore  the  magician's  wand  which  links  particles 
together  in  various  ways  and  so  makes  them  appear  to  our 
eyes  and  other  senses  as  very  different  things. 

Whoever  would  have  thought  that  the  black  stuff  which 
comes  out  of  bread  when  it  is  badly  toasted  is  in  the  white 
substance  called  flour.  This  tells  us  then  that  chemical 
force  which  joins  things  together  can  turn  black  into  white, 
and  when  heat  overcomes  this  chemical  force  it  can  turn 
white  into  black.  The  black  and  white  of  course  are 
different  substances. 

A  chemist  can  take  this  black  substance  which  is  got  out 
of  bread,  and  by  melting  it  and  tightly  pressing  it  together  in 
a  suitable  vessel  at  a  very  high  temperature,  near  the  melting- 
point  of  iron,  turn  it  into  a  diamond. 

He  adds  nothing  to  it,  nor  does  he  take  anything  away, 


Substances  and  their  Changes.  209 

but  the  heat  rearranges  the  particles  originally  forming  the 
black  material,  and  that  which  was  black  and  opaque  be- 
comes brilliant  and  transparent.  It  is  no  more  wonderful 
than  the  aniline  dye  manufacturer,  who  starting  with  tar, 
as  is  used  in  street  paving,  turns  it  into  beautiful  dyes. 

Changes  in  Electricity, 

The  changes  which  go  on  in  substances  when  by  their 
acting  upon  one  another  new  substances  are  produced  is  no 
more  remarkable  than  the  changes  which  electricity  may 
undergo. 

Consider  a  tram-car  driven  and  illuminated  by  electricity. 
The  same  electricity  that  leaves  the  overhead  wire  enters 
the  mechanism  of  the  car  and  sets  it  in  motion  is  also 
converted  into  light  and  heat.  Here  is  a  wonderful  trans- 
formation of  electricity  into  motive  power,  heat,  and  light ; 
new  creations,  as  it  were,  from  the  original  one. 

Light  and  heat  thus  have  their  origin  from  electricity, 
and  other  remarkable  changes,  such  as  friction  producing 
heat  and  heat  producing  electricity,  are  of  constant  occur- 
rence. 

It  is  just  as  difficult  to  see  the  causes  or  way  by  which 
electricity  changes  and  becomes  heat  as  it  is  to  see  the 
causes  or  way  by  which  substances  change  when  they  act 
together  and  give  rise  to  new  substances. 

Practical  Application  to  Mining, 

In  the  previous  pages  of  this  chapter  it  has  been  ex- 
plained how  changes  are  continually  taking  place  due  to  the 
constant  state  of  war  which  exists  between  the  various  sub- 
stances forming  the  world. 

Those  who  work  in  mines  may  find  in  their  daily  experience 
many  examples  of  these  changes.  When  lamps  burn,  or 
men  breathe,  the  strife  between  the  oxygen  of  the  air  and 
the  carbon  of  the  lamp  oil  or  the  human  body  results  in 
the  formation  of  a  new  substance  called  carbon  dioxide. 
This  substance  is  composed  of  carbon  and  oxygen  but 
possesses  the  properties  of  neither,  which  will  explain  what 
often  puzzles  beginners — why  a  substance  containing  so 
much  oxygen  is  dangerous  to  breathe.  It  should  be 

14 


2io         An  Introduction  to  Mining  Science. 

remembered  that  in  the  dark  passages  of  the  mine  there  is 
no  compensating  change  as  on  the  surface,  where  the  action 
between  carbon  dioxide  and  plants  in  the  presence  of 
sunlight  results  in  the  absorption  of  carbon  dioxide  and  the 
giving  out  of  oxygen.  The  change  is  entirely  one  of  produc- 
tion due  partly  to  burning  and  breathing  and  partly  to  action 
between  the  coal  and  the  air,  and  if  it  were  not  for  the  fresh 
air  which  is  constantly  being  circulated  through  the  mine  the 
atmosphere  would  soon  become  so  changed  as  to  be  unfit 
for  breathing. 

When  explosives  containing  nitro-glycerine  are  imperfectly 
detonated  or  allowed  to  burn  without  detonating,  the  con- 
stituents of  the  explosive,  particularly  the  oxygen,  attack 
each  other,  and  the  result  is  the  formation  of  new  gases 
which  are  very  dangerous  to  breathe. 

When  explosives  of  any  description  are  fired  change 
takes  place  and  the  solid  explosive  is  changed  into  gases 
which  have  different  properties  from  those  of  the  solid  from 
which  they  came. 

Further  examples  of  familiar  changes  which  occur  in  mining 
experience  are : — 

1.  The  action  of  water  on  steam  boilers.     A  hard  crust 
of  scale  is  often  formed  on  the  inside  of  boilers  by  the  im- 
purities  contained   in    the   feed   water.     To   remedy   this 
further   impurities  are  often  added  to  the  water  with   the 
object  of  setting  up  action  between  the  various  impurities, 
resulting  in  the  formation  of  new  bodies  with  less  injurious 
properties. 

2.  Grease  in  boilers  or  engine  cylinders  may  be  a  means 
of  setting  up  chemical  action,  causing  corrosion  and  pitting 
of  the  boiler  plates. 

3.  Tubbing  used  in  pit  shafts  and  pipes  conveying  water 
to  and  from  pumps  are  often  acted  upon  by   substances 
contained  in  the  water.     Sometimes  the  pipe  may  get  so 
soft  that  it  can  be  cut  by  a  knife. 

4.  Changes  occur  in  the  Leclanche  cells  often  used  for 
providing  the  electricity  for  signalling  purposes  in  mines. 
The  zinc  rod  is  eaten  away  and  the  liquid  in  the  cell  be- 
comes entirely  changed  in  the  course  of  time,  having  entirely 
different  properties. 


Substances  and  their  Changes.  211 

Still  further  examples  of  these  wonderful  changes  will 
doubtless  present  themselves  to  the  observant  student  as  he 
goes  about  his  work. 

QUESTIONS. 

1.  Ordinary  air  may  be  turned  into  liquid  nitric  acid  by  electricity, 
therefore  both  are  made  of  the  same  substances.     What  name  would 
you  give  to  this  change  ?     Such  changes  of  substances  being  turned 
into  other  different  substances  are  very  common ;  try  and  mention  some. 

2.  Give  reasons  for  saying  that  new  things  are,  or  are  not,  produced 
when  the   following  actions   occur:  (i)  iron  is  rusted;    (2)  wood  is 
burnt ;  (3)  electricity  is  passed  through  an  electric  lamp ;  (4)  water  is 
boiled  ;  (5)  gunpowder  is  exploded. 

3.  What  is  meant  by  the  by-products  of  coal  ?     If  there  be  a  by- 
product plant  in  your  district,  try  and  find  the  names  of  the  different 
substances  made  from  coal,  and  what  becomes  of  them. 

4.  How  many  things  are  produced  when  petrol  burns  ?     What  are 
the  changes  it  undergoes  ? 

5.  When  carbide  of  calcium  is  treated  with  water  acetylene  gas  is 
formed.     Why  is  it  certain  that  the  carbide  has  undergone  a  change  ? 

6.  Give  the  names  of  the  substances  into  which  the  following  may 
be  changed,  and  state  how  the  change  is  brought  about :    limestone, 
soil,  wood,  bread,  oil,  air,  and  milk. 


CHAPTER  XIV. 
COAL,  ITS  NATURE,  PRODUCTS,  AND  ORIGIN. 

WHEN  coal  is  being  burnt  great  changes  are  going  on  in  it, 
and  the  final  result  is  material  called  ashes,  which  are  left 
in  the  grate,  and  a  great  deal  of  smoke,  and  gas,  which  have 
gone  up  the  chimney. 

Smoke  and  soot  are  two  very  visible  things  produced  in 
the  change,  but  they  do  not  form  the  whole  of  the  substances 
which  pass  up  the  chimney  flue ;  there  are  invisible  gases 
mixed  with  the  rising  smoke.  These  invisible  gases  are 
worth  a  consideration ;  they  will  bring  out  the  value  of  air  in 
the  changes  going  on  in  the  fire-grate. 

Experience, 

Attention  should  be  given  to  the  smoke  issuing  from  different 
chimneys  :  factory,  mine,  and  house.  In  some  cases  it  will  be 
found  black,  in  other  cases  white. 

It  should  be  clearly  realized  that  coming  from  such 
chimneys  along  with  the  visible  smoke  there  are  invisible 
gases,  chiefly  non-combustible  ones,  otherwise  the  smoke 
might  be  accompanied  by  flame.  These  incombustible 
gases  are  carbon  dioxide,  oxygen,  and  nitrogen.  There 
may  be  a  small  amount  of  carbon  monoxide  in  the  smoke, 
but  it  is  too  cool  and  too  dilute  to  burn  at  the  chimney  top. 

The  difference  between  black  and  white  smoke  is  really 
caused  by  bad  and  good  combustion.  In  the  former  case 
there  is  too  low  a  temperature  or  too  bad  a  draught  to 
get  good  combustion,  and  some  soot  particles  get  through 
unburnt. 


Coal,  its  Nature,  Products,  and  Origin.       213 

How  Combustion  is  Helped, 

Why  is  the  fire  lifted  up  by  the  poker  ?  It  is  to  let  air 
into  the  interior  of  the  fire  so  that  combustion  may  be 
increased;  the  poker  is  also  used  to  remove  the  ash  which 
chokes  up  the  entrances  through  which  the  air  should  pass. 

Experience, 

Take  off  the  lamp  glass  of  a  burning  oil  lamp  and  notice  the 
incomplete  combustion,  there  is  smoking,  caused  by  too  bad  a 
draught.  The  lamp  glass  improves  the  air  supply.  Opening 
and  closing  the  damper  of  the  chimney  gives  similar  effects. 

Sometimes  the  amount  of  oxygen  in  chimney  smoke 
may  be  as  much  as  17  per  cent,  but  in  fires  stoked  by 
machinery  it  may  be  as  small  as  6  per  cent  (see  Table, 
p.  217);  a  whiter  smoke  is  produced  by  the  extra  oxygen 
having  been  used  in  burning  carbon  particles.  A  white 
smoke  means  no  waste  of  the  heating  power  of  coal,  whereas 
a  black  smoke  means  great  loss.  In  the  City  of  London  it 
is  said  that  76,000  tons  of  soot  are  given  off  annually  into 
its  air ;  this  means  a  great  loss  of  heating  power. 

The  Smut, 

That  black  irritating  coal-flake  produced  when  combustion 
is  very  bad,  called  the  smut,  is  worth  a  little  consideration ; 
it  is  sticky,  light,  combustible,  and  acid.  These  are  four 
properties  of  the  smut  which  will  teach  us  a  lesson  in 
chemistry  from  experience  and  experimental  points  of  view. 
The  stickiness  is  due  to  a  small  amount  of  tar  in  the  smut, 
and  so  it  collects  on  the  surroundings  of  the  fire-grate. 
Look  at  the  back  of  the  fire-grate  and  notice  how  it  is 
plated  over  with  soot,  and  further  notice  that  when  a  big 
fire  is  burning  this  soot  gets  burnt  away,  and  the  red  colour 
of  the  bricks  of  the  fire  back  are  again  seen,  so  the  smut  is 
combustible.  That  such  is  the  case  is  shown  each  time  "  a 
chimney  gets  on  fire  ". 

The  smut  is  light ;  it  floats  on  water  and  goes  along  with 
a  light  breeze  of  air ;  in  this  it  resembles  a  snow-flake. 

Experiment. 

Take  a  small  amount  of  soot  and  throw  it  on  some  water  in  a 
dish  ;  it  floats.  Stir  it  up  with  the  water  and  then  dip  in  a  blue 


214          An  Introduction  to  Mining  Science. 

litmus  paper ;  if  the  blue  colour  changes  to  red  then  the  liquid 
is  acid,  the  acid  comes  from  the  smut. 

Coal  contains  a  small  amount  of  sulphur  (brimstone)  which 
on  burning  turns  to  an  acid ;  in  a  fog  of  the  smoky  variety 
the  eyes  often  smart,  and  the  mouth  tastes  its  acidity. 

Combustible  Gas  Mixed  with  Smoke, 

A  fire  may  be  almost  out,  or  at  least  shows  only  signs  of 
a  red  glow  at  parts,  but  nevertheless  gas  and  smoke  may  be 
coming  off  from  the  coal.  A  fire  fed  by  Silkstone  coal  often 
shows  this  state,  and  the  following  experiment  may  be 
performed. 

Experiment, 

Drop  a  lighted  match  on  to  the  fire  in  the  grate  where  smoke 
is  coming  off;  the  gas  mixed  with  the  smoke  may  ignite.  If  it 
does,  it  proves  the  presence  in  it  of  combustible  gas. 

This  is  a  very  important  point.  It  tells  us  that  the  heat  of 
the  coal  is  too  low  in  temperature  to  ignite  the  gas,  but  the 
temperature  of  the  match  is  high  enough.  Therefore  the 
temperature  at  which  coal  gas  ignites  must  be  reached 
before  a  flame  results. 

The  Arrangement  of  a  Coal  Fire, 

A  fire  which  is  ready  for  lighting  usually  consists  of  three 
distinct  layers  :  a  layer  of  paper  at  the  bottom,  then  a  layer 
of  wood  or  chips,  and  a  coal  layer  at  the  top.  Notice  that 
the  materials  are  of  different  thicknesses ;  thin  paper, 
thicker  wood,  and  pieces  of  coal. 

Why  should  there  be  such  a  series  of  layers?  It  is 
connected  with  the  fact  that  the  burning  has  to  be  started 
by  a  match  which  has  but  a  very  short  life  as  a  fire-giver 
and  therefore  cannot  be  used  to  ignite  the  coal  directly. 

The  layers  of  paper  and  wood  are  sometimes  done  away 
with  and  "  firelighters "  used,  as  the  latter  are  made  of 
bits  of  wood  and  an  inflammable  material,  and  as  the 
ignition  is  started  by  a  lighted  match  setting  on  fire  firstly 
the  easily  inflammable  material  and  then  the  wood,  the 
problem  is  much  like  the  three  layers  of  the  fire. 


Coal,  its  Nature,  Products,  and  Origin.       21$ 

The  paper  is  easily  ignited,  much  more  easily  than  wood, 
and  very  quickly  is  all  ablaze.  The  burning  paper  is 
sufficiently  hot  to  ignite  the  wood  but  lasts  a  very 
short  time  compared  with  the  latter.  When  the  wood  gets 
into  action  there  is  an  abundance  of  heat  produced,  and  as 
it  lasts  for  some  time  the  coal  gets  warmed  up  and  finally 
ignites.  It  is  not  until  the  temperature  of  the  coal  ap- 
proaches 350°  C.  that  there  is  any  indication  of  burning. 
The  temperature  at  which  burning  takes  place  varies 
slightly  with  the  quality  of  the  coal,  but  as  soon  as  it  gets 
higher  than  350°  C.  rapid  action  begins. 

Other  Phenomena  of  the  Coal  Fire. 

As  the  coal,  particularly  a  soft  one,  gets  hot  it  cakes,  or 
becomes  pasty,  and  at  these  pasty  places  "  blowers  of  gas  " 


FIG.  98. — A  blower. 

will  be  formed,  and  as  this  gas  issues  out  it  will  light.  If  the 
fire  is  very  hot  the  gas  may  be  ignited  throughout  from  A 
to  B. 

The  flame  will  often  be  limited  to  the  end  A  and  not 
be  burning  its  full  length,  AB.  Gas  is  then  being  distilled 
off  too  rapidly  to  allow  the  flame  striking  back  to  B,  and  no 
air  being  mixed  with  it  at  B  it  cannot  burn.  Moreover,  as 
the  gas  rushes  out  and  expands  it  gets  cool  and  this  hinders 
its  ignition. 

Notice  the  variations  in  the  shape  of  the  flame  and  its 
irregularity,  the  orifice  from  which  it  issues  varies  in  shape  ; 
so  the  shape  of  the  flame  is  dependent  upon  the  orifice  it 
issues  through.  Variations  of  the  pressure  with  which  the 
gas  forces  itself  out  also  influences  the  shape. 

The  flame  may  often  be  seen  to  be  brighter  at  the  base 
than  at  the  free  end  ;  this  is  due  to  the  heat  of  the  hot  coal 


216          An  Introduction  to  Mining  Science. 

helping  the  luminosity ;  a  heated  gas  burns  more  brightly 
than  a  cool  one. 

The  Gases  Found  Burning  in  a  Coal  Fire, 

The  gases  which  burn  in  the  fire  may  be  divided  into 
two  groups : — 

1.  Those  present  in  the  coal  just  as  it  comes  from  the  pit. 

2.  Those  which  are  formed  as  the  coal  is  heated  by  the 
fire,  and  do  not  exist  originally  in  the  coal. 

To  the  first  group  belong  marsh  gas  and  the  gas 
nitrogen.  Nitrogen  is  not  a  combustible  gas,  so  it  does 
not  burn  in  the  fire,  whereas  marsh  gas  burns  with  a  very 
pale  blue  non-luminous  flame.  The  latter  gas  may  often  be 
seen  to  take  fire  when  a  piece  of  coal  splits  along  the  grain 
by  the  heat  of  the  fire.  Hydrogen  only  occasionally  occurs 
in  coal ;  if  present,  it  would  burn  with  a  colourless  non- 
luminous  flame. 

Experience, 

Watch  a  piece  of  coal  in  the  fire,  and  when  it  is  beginning  to 
burn  well  split  it  along  the  grain.  Very  often  a  pale  blue  flame 
will  run  between  the  separated  faces  of  the  coal ;  this  is  marsh 
gas  burning.  Very  occasionally  it  may  be  hydrogen  which  has 
a  colourless  flame ;  it  is  difficult  to  distinguish  between  it  and 
marsh  gas  by  their  appearances  when  burning. 

The  second  group  comprises  coal  gas  and  carbon 
monoxide.  Coal  gas  is  a  mixture  of  different  gases  (see 
p.  155),  and  when  burning  is  easily  recognized  by  the  familiar 
yellow  flame;  it  is  seen  in  the  fire  as  soon  as  the  coal  gets 
hot  enough  to  decompose  and  form  the  gas.  The  yellow 
part  of  the  flame  is  due  to  the  burning  of  a  gas  called 
ethylene ;  the  burning  of  marsh  gas  and  hydrogen  help  to 
form  the  blue  part  of  the  flame. 

Carbon  monoxide  gas  occurs  in  fires  as  pointed  out  on 
p.  in.  It  is  formed  in  two  ways  on  an  ordinary  coal  fire. 
In  the  first  place  the  decomposition  of  the  coal  by  heat 
produces  a  small  quantity  of  carbon  monoxide,  and  this 
occurs  when  the  fire  is  not  entirely  red-hot.  When  the  fire 
is  red-hot  throughout  carbon  dioxide  is  being  produced,  but 


Coal,  its  Nature,  Products,  and  Origin.       217 

before  it  leaves  the  red-hot  area  it  is  quickly  robbed  of  half 
of  its  oxygen  and  becomes  carbon  monoxide  (see  p.  113). 

Carbon  dioxide  occurs  in  neither  group  because  it  is  not 
found  burning  in  a  coal  fire  ;  it  is  incombustible.  Of  course 
carbon  dioxide  is  formed,  and  as  long  as  it  is  being  formed 
the  coal  or  coal  gases  are  burning,  but  as  soon  as  their  car- 
bon has  turned  into  carbon  dioxide  their  career  of  burning 
is  ended. 

The  following  figures  show  the  gases  and  the  proportion 
in  which  they  are  to  be  found  in  a  well-burnt  flue  gas : — 

Carbon  dioxide  .     11*2  per  cent. 

Oxygen    .          .  .8-4      „ 

Carbon  monoxide  .       IT       „ 

Nitrogen  .     79-3       „ 

lOO'O 

Nitrogen  is  in  the  biggest  quantity  because  it  is  plentiful 
in  the  air  which  supplies  the  oxygen  for  combustion.  The 
nitrogen  does  not  undergo  combustion.  The  oxygen  of  the 
air  is  reduced  in  quantity  because  it  is  used  in  burning  the 
coal,  or  coal  gases,  into  carbon  monoxide  and  carbon 
dioxide  ;  the  former  gas  is  very  small  in  amount. 

The  Origin  of  Coal, 

There  seems  to  be  very  little  resemblance  between  coal 
and  that  of  the  vegetation  of  a  great  forest,  yet  it  is  said  to 
have  been  produced  gradually  from  trees  and  plants  of  various 
shapes  and  sizes,  their  leaves,  roots,  stems,  and  branches, 
which  grew  in  a  low  marshy  district  with  a  warm  moist 
climate  (see  Fig.  99).  This  vegetation  long  years  ago  grew, 
died,  accumulated,  and  was  finally  covered  by  great  quan- 
tities of  rock.  As  a  matter  of  fact,  impressions  of  plants 
and  trees,  or  their  parts,  which  were  being  sealed  up  as 
the  vegetation  was  rotting  and  before  the  overlying  rocks 
were  being  laid  down,  are  often  found  when  coal  is  split 
along  its  layers.  In  a  wood  or  coppice  to-day  may  be 
seen  trees  which  have  fallen,  and  there  is  evidence  that 
this  occurred  in  forests  of  the  Coal  Age ;  the  time  when 
coal  was  vegetation.  The  roof  of  the  coal  seam  also 


Coal,  its  Nature,  Products,  and  Origin.       219 


contains  the  upright  stems  of  trees.  Fig.  100  shows  a 
stone  cast  of  the  stem  and  roots  of  a  tree  very  common 
in  the  coal  seams.  Two  most  conspicuous  differences 
between  coal  and  vegetation  are  colour  and  compact- 
ness. These  differences  should  not  as  regards  the  origin 
of  coal  present  any  difficulty  to  us,  because  the  green  leaves 
of  the  tobacco  plant  are  by  the 
tobacco  manufacturer  turned  into 
various  shades  of  brown  to  jet 
black,  and  by  pressure  they  are 
shaped  into  thin  layers  called  cake 
tobacco.  The  influences  which 
help  to  bring  about  such  colour 
changes  quickly  are  very  similar 
to  those  which  helped  in  the  al- 
teration from  vegetation  to  coal. 
In  producing  the  blackening  of 
cake  tobacco  the  leaf  is  kept  warm 
and  under  pressure.  Coal  seams 
in  the  making  were  at  a  great 
depth  subjected  to  a  higher  tem- 
perature than  vegetation  on  the 
earth's  surface,  and  even  what  are  now  seams  near  the  sur- 
face have  been  much  deeper  down  in  former  centuries. 
The  tobacco  manufacturer,  it  is  true,  uses  small  quantities 
of  oil  to  help  in  the  blackening  of  the  tobacco  leaf,  but  oil 
is  found  in  vegetation  to  a  more  or  less  extent,  and  so  may 
have  helped  in  the  blackening  process.  Resin,  which  is 
related  to  oils,  is  found  in  coal. 

Leaves  that  fall  on  the  roadsides  in  autumn  and  gradually 
rot  as  winter  approaches  go  through  many  shades  of  colour 
as  they  become  black.  Sycamore  leaves,  almost  perfect  in 
shape  but  black  in  colour,  are  not  uncommon  to  the  obser- 
vant walker  in  country  lanes  ;  the  black  substance  of  which 
the  leaf  consists  is  much  akin  to  coal. 

Suppose  we  go  into  a  wood  or  coppice  and  at  the  foot  of 
a  tree  clear  away  the  accumulated  remains  of  twigs,  leaves, 
etc.,  which  have  fallen  from  the  tree  for  many  years,  it  will 
be  noticed  that  the  deeper  we  dig  down  the  blacker  the 
remains  are,  and  the  freer  from  any  shape  or  form.  Pres- 


FIG.  100. 


220         An  Introduction  to  Mining  Science. 

sure  acting  upon  these  remains  would  help  to  make  them 
more  like  coal. 

The  middle  parts  of  hay-stacks  often  show  a  dark  brown 
colour  owing  to  internal  heating,  and  the  pressure  compacts 
the  hay  into  layers. 

Just  as  pressure  of  overlying  hay  compacts  the  underpart 
and  makes  well-defined  layers,  so  all  the  original  loose 
covering  over  the  vegetation  of  the  Coal  Age  forests  ;  the 
soil  in  which  the  trees  grew,  and  the  vegetation  itself  have 
been  by  overlying  rock  material  turned  into  layers  of  rock 
and  coal  (see  b,  d,  a,  Fig.  101). 


; 


FIG.  101. — a,  coal  seam  ;  d,  under-clay ;  b,  c,  shale  and  sandstone 
forming  roof. 

The  figure  shows  the  rocks  which  are  passed  through  in 
many  pits  when  going  from  the  surface  to  the  coal  seam,  a. 
Under  the  coal  is  the  pit  floor,  a  layer,  d,  of  "  under-clay/'  as 
it  is  called  ;  it  has  hardened  into  shale,  and  in  it  are  found  the 
roots  of  trees  which  grew  in  the  forests  of  the  Coal-forming 
Age.  The  roof  of  the  coal  seam  is  shown  at  l>,  and  may  be  a 
layer  of  shale  or  other  kind  of  rock ;  in  it  are  often  found 
stems  and  branches  of  trees. 

A  great  depth  gives  a  great  pressure,  and  even  at  a  depth 
of  1000  feet  below  the  earth's  surface  there  would  be  a  pres- 
sure of  about  74^  tons  on  a  square  foot.  This  pressure  acting 
on  a  mass  of  vegetation  would  in  time  make  it  undergo 
great  changes. 


Coal,  its  Nature,  Products,  and  Origin.       221 

This  figure  is  arrived  at  in  this  way  :  a  cubic  foot  of  water 
weighs  62^  Ibs.  and  rock  is  2^  times  heavier  than  water,  and 
so  we  get  i66j  Ibs.  per  cubic  foot,  and  a  column  of  1000  feet 
of  this  in  length  and  a  square  foot  in  section  would  weigh 
166,250  Ibs. 


FIG.  102. — Showing  the  method  of  producing  gas  by  heating  coal  or 

wood. 

Experimental    Evidence   of  the    Similarity    between 
Wood  and  Coal.     Dry  Distillation  of  Substances, 

Fit  a  hard  glass  test  tube  (Fig.  102)  with  a  cork,  through  which 
passes  a  fine  glass  tube.  Introduce  into  the  test  tube  a  few  bits 
of  coal  and  then  heat  strongly  in  the  Bunsen  flame.  Gas  will  be 
given  off,  which  may  be  ignited  at  the  mouth  of  the  tube.  To 
establish  it  as  a  gas  collect  some  in  an  inverted  test  tube  or  gas 
cylinder  full  of  water. 

Take  the  vessel  used  for  collecting  the  gas  and,  keeping  it 
inverted,  apply  a  light  to  the  gas  ;  it  will  burn  with  the  familiar 
yellow  flame. 

In  the  water  through  which  the  gas  has  passed  place  a  bit  of 
red  litmus  paper  ;  it  will  become  blue  if  ammonia  is  present, 
which  is  also  denoted  by  the  smell.  The  water  will  contain  a 
tarry  substance,  and  coke  will  be  left  in  the  tube. 


222          An  Introduction  to  Mining  Science. 

Repeat  the  experiments  with  coke  and  wood.  The  wood  and 
coke  should  be  in  small  bits. 

Dry  distillation  means  that  the  substance  is  being  heated 
out  of  contact  with  air,  and  the  substances  so  formed  are 
distilled  out  of  the  vessel. 

Some  of  the  foregoing  substances  derived  from  coal  are 
called  "  by-products,"  and  they  are  worked  up  industrially 
to  make  sulphate  of  ammonia  and  coal-tar  compounds 
such  as  dyes. 

In  the  case  of  wood  the  water  will  be  found  acid,  and 
therefore  a  blue  litmus  paper  will  be  turned  red ;  this  acid  is 
the  one  found  in  vinegar. 

The  following  figures  show  the  quantities  of  various  sub- 
stances obtained  in  dry  distillation  of  wood  and  coal : — 

Substances.  Percentages  by  Weight. 

Wood.  Coal. 

Gas 25  to  28          14  to  17 

Substances  which  condense   .         .     45  ,,  50         12  „  23 
Charcoal  or  coke  .         .         .         .     25  „   27         60  „   74 

The  coke,  charcoal  in  the  case  of  wood,  is  left  behind 
unburnt  because  there  is  no  air  in  the  tube.  If  either  were 
heated  in  the  presence  of  air  they  would  burn  completely 
away,  except  any  ash  left  behind. 

Experience. 

The  coke  of  the  watchman's  fire  burns  away  leaving  only  an 
ash  ;  trees,  wood,  and  stubble  when  fired  burn  completely  away, 
except  for  leaving  an  ash.  No  charcoal  is  left  behind  because 
the  burning  is  in  the  open  air,  which  supplies  oxygen  unlimited 
in  amount. 

If  coal  and  wood  are  similar  substances,  then  we  might 
expect  that  the  composition  of  coal  gas  and  wood  gas  would 
be  very  similar.  Their  components  given  in  the  following 
table  show  there  is  similarity  : — 

Coal  Gas.  Wood  Gas. 

Hydrogen         52-9  per  cent.  1 8  to  42  per  cent. 

Marsh  gas         31-8       „  9  „  35       „ 

Ethylene             4-4       „  9  „  35 


Coal,  its  Nature,  Products,  and  Origin.       223 

The  numbers  representing  the  per  cent  is  the  number  of 
cubic  feet  of  that  gas  in  100  cubic  feet  of  coal  or  wood  gas. 
The  three  gases  mentioned  nearly  make  100  per  cent. 

The  other  gases  found  in  small  quantities  are  nitrogen, 
carbon  monoxide,  etc. 

The  gases  therefore  are  the  same  and  differ  only  in  the 
amounts  mixed  together;  hydrogen  and  marsh  gas  are 
abundant.  Ethylene  helps  the  luminosity  of  the  gases; 
the  first  two  burn  without  luminosity. 

The  chief  interest  to  us  is  the  presence  of  marsh  gas  in 
both  the  gases. 

This  gas  is  produced  by  the  changes  which  go  on  in  the 
wood  and  coal  when  heated,  but  the  same  change  goes  on 
only  much  more  slowly  in  coal  seams,  which  of  course  are 
cut  off  from  air,  and  in  wood  undergoing  decomposition 
where  air  is  absent. 

The  fact  that  both  wood  and  coal  give  off  marsh  gas  when 
decomposed  quickly  by  heat  or  slowly  by  a  kind  of  rotting, 
and  in  each  case  in  the  absence  of  air,  suggests  they  are  made 
of  the  same  material. 

The  following  figures  show  the  elements  and  their  quanti- 
ties found  in  different  stages  of  vegetation  and  coal,  and 
afford  evidence  of  the  transformation  of  wood  into  coal : — 

Composition  by  Weight. 

Elements.      Dried       Peat.     Brown      Coal. 
Wood.  Coal. 

Carbon  50  58  66  84  per  cent. 

Hydrogen  6  5  5  5  „ 
Oxygen   i 

Nitrogen}  44  37  *9  «  .. 

The  figures  tell  this  story  :  that  as  wood  has  changed  to 
peat  and  then  to  brown  and  finally  black  coal  it  has  lost 
some  of  the  three  last-mentioned  substances.  These  three 
substances  are  all  gases  and  therefore  get  away,  but  carbon 
is  a  black  non-volatile  solid,  and  like  similar  solids  it  cannot 
get  away.  Hence  as  wood  changes  into  coal  it  gets  richer 
in  carbon, 


224         An  Introduction  to  Mining  Science. 

Practical  Application  to  Mining. 

The  teaching  of  the  coal  fire  is  of  very  great  importance 
to  those  who  hope  to  and  may  eventually  have  the  manage- 
ment of  collieries,  and  also  to  those  who  have  to  attend  to 
the  boilers  generating  steam  at  the  surface  of  the  mine. 

A  boiler  fire  badly  tended  or  not  getting  sufficient  air  is 
a  wasteful  thing.  It  also  causes  black  smoke  to  pour  out 
of  the  chimney,  blackening  and  spoiling  the  beauty  of  the 
surrounding  country. 

Sometimes  the  natural  draught  due  to  the  chimney  is  poor 
and  insufficient  to  enable  the  fire  to  get  its  proper  supply  of 
air.  In  this  case  if  efficiency  is  to  be  obtained  the  draught 
must  be  improved  by  lengthening  the  chimney,  or  by  plac- 
ing a  fan  in  the  base  of  the  chimney  or  by  some  other  method 
of  forced  draught.  Even  under  the  best  conditions  known 
in  modern  engineering  practice  the  driving  of  engines  by 
steam  generated  from  coal  in  steam  boilers  is  not  economi- 
cal, only  a  very  small  percentage  of  the  heat  energy  stored 
in  the  coal  being  available  for  doing  useful  work. 

When  the  conditions  are  bad  the  percentage  efficiency  is 
very  low  indeed. 

In  our  coal  fire  we  get  cinder  or  coke,  and  the  business 
of  making  coke  is  a  large  and  ever-increasing  one  at  many 
of  our  collieries. 

Coke  is  used  in  blast  furnaces  for  the  making  of  iron  and 
steel  and  for  other  purposes.  When  coal  is  heated  in  the 
absence  of  air,  or  with  only  a  very  small  quantity  of  air, 
it  undergoes  great  changes.  The  gases  are  distilled  off  in 
various  forms  and  a  solid  substance  remains  which  we  call 
coke.  It  consists  chiefly  of  carbon  and  the  ash  of  the  coal, 
but  sometimes  contains  small  quantities  of  other  substances. 

When  the  coal  is  distilled  in  the  entire  absence  of  air  the 
ovens  used  are  called  retort  ovens.  An  oven  consists  of  a 
chamber  surrounded  by  a  number  of  flues  or  passages. 
The  coal  is  placed  in  the  oven  which  is  then  sealed  up 
tightly,  the  heat  for  heating  the  coal  being  obtained  by 
burning  gas  in  the  flues. 

When  a  small  amount  of  air  is  admitted  ovens  of  the 
Beehive  type  are  employed.  This  oven  is  a  dome-shaped 


Coaly  its  Nature,  Products,  and  Origin.       225 

chamber  having  a  doorway  in  front  through  which  the  coke 
is  taken  from  the  oven,  and  an  opening  at  the  top  for  putting 
in  the  coal.  A  flue  and  a  chimney  are  also  necessary.  The 
opening  at  the  top  of  the  oven  is  closed  by  an  iron  lid  or 
damper.  The  door  in  front  js  closed  by  means  of  bricks 
and  soft  clay,  a  small  opening  being  left  for  the  admission 
of  air. 

By-Products. 

The  story  of  a  piece  of  coal  is  truly  a  wonderful  one. 
In  addition  to  giving  us  heat  and  light,  and  power  in  the 
form  of  steam,  it  is  now  possible  to  collect  the  products  given 
off  in  the  making  of  coke,  and  by  putting  them  through  vari- 
ous processes  to  get  from  them  such  substances  as  tar, 
ammonia,  and  benzol.  Benzol  is  now  largely  used  instead 
of  petrol  in  motor-cars ;  from  tar  many  beautiful  colours  and 
dyes  used  in  beautifying  our  homes  and  our  dress  are  ob- 
tained. 

QUESTIONS. 

1.  Compare  the  result  of  heating  wood  in  a  closed  vessel  and  heat- 
ing it  in  the  open  air. 

2.  The  best  calcium  carbide  gives  5  cubic  feet  of  acetylene  gas- 
per  Ib.     Compare  this  with  the  amount,  10,000  cubic  feet,  of  coal  gas 
given  by  a  ton  of  coal. 

3.  Explain  the  formation  of  jets  of  gas — blowers — and  bubbles  of 
tarry  material  on  coal  after  it  is  placed  on  a  fire. 

4.  One  hundred  oz.  of  coal  left  4  oz.  of  ash  when  burnt  in  air.    When 
heated  away  from  air  100  oz.  of  the  same  coal  left  go  oz.  of  coke. 
Find  the  amount  of  combustible  material  in  (i)  the  coal,  (2)  the  coke. 
What  would  be  the  nature  of  the  material  lost  by  the  coke  ? 

5.  How  would  you  show  that  coal  gas  is  lighter  than  air  ? 

6.  Give  a  description  of  the  different  kinds  of  coal  and  coal  seams 
found  in  your  mine.     Why  should  you  sort  coal  into  a  part  for  selling 
and  a  part  for  the  pit  heap  ? 


INDEX. 


ABSORPTION  of  substances,  29. 


Accidents  in  mines, 
188,  190. 


12,  125,  175, 


After-damp,   composition    of,  119, 

122. 

—  formation  of,  119, 

Air,  action  on  phosphorus,  17. 

—  crossing,  59. 

—  currents  of,  44,  45,  54. 

—  its  composition,  22,  23. 
-  its  constituents,  21. 

—  in  mines,  57,  63. 

—  its  weight,  47,  48. 

Air  supply,  its  effect  on  combus- 
tion, 16. 

Altoft's  experiments,  158. 
Aluminium  carbide,  109. 
Ammonium  dichromate,  183. 
Anemometer,  64. 

BLACK-damp,  its  composition,  120, 

122,  124. 
Blowers,  215. 
Boiling-point,  169. 

—  of  water,  77. 
Boyle,  Robert,  21. 
Breathing,  gases  given  off,  30. 
Bunsen,  von  R.,  149. 

Bunsen  burner,  in  industry,  150. 
its  structure,  149. 

—  flame,    proportions  of  gas  and 

air,  151. 

structure,  152,  153. 

section  of,  152. 

temperature,  153,  154. 

unburnt  core,  153. 

Burners,  bat's-wing  and   fish-tail, 
144. 

CALCIUM  carbide,  no. 

—  carbonate,  29. 


Calcium  oxide  (lime),  29. 

—  phosphide,  168. 
Candle-power,  meaning  of,  144. 
Carbon,  in  flames,  144. 

—  well-known  forms,  146. 
Carbon  dioxide,  detection,  30. 

diffusion,  35. 

extinguishing  power,  34. 

heaviness,  34. 

in  air,  37. 

preparation,  32. 

Carbon  disulphide,  171. 

Carbon  monoxide,  effects  on  man, 

115. 
from  carbon  dioxide,  112. 

—  —  in  mines,  115. 
its  making,  114. 

occurrence,  in,  113,  216. 

properties,  115. 

Carbon  oxides,  in  fires,  113. 

their  changes,  112. 

Change  of  condition,  204. 
Chemical  action,  163. 

—  change,  210. 
in  matches,  164. 

—  force,  203.  * 
Choke-damp,  105. 
Classification  of  substances,  207. 
Coal,  gases  given  off  from,  121. 

—  gases  in,  216. 
-  its  origin,  217. 

Coal  fire,  its  arrangement,  204. 
Coal  gas,  its  composition,  155,  222. 

its  mixing,  192. 

Cohesion,  204. 

Combustion,  changes  during,  4. 
—  cause  of,  6. 

—  heat  production,  6. 

—  in  pit,  12. 

—  its  rusting  form,  3. 


227 


228  An  Introduction  to  Mining  Science. 


Combustion,  quickness  of,  i. 

—  spontaneous,  3. 
Conduction  of  heat,  by  metals,  80. 

order  of  ease,  gi. 

Convection  currents,  in  air,  49,  72, 

8.7,  97- 

in  liquids,  98. 

in  ventilation,  97. 

round  lamps,  85. 

Cooling  by  evaporation,  86. 

—  its  action  on  bodies,  68-69. 
Currents  of  air,  by  heat,  44,  45. 
by  rarefaction,  53. 

DAMPS,  composition  of,  120-122. 
Davy,  Sir  Humphrey,  84. 
Density,  of  gases,  53,  118. 

—  of  liquids,  194. 

—  its  meaning,  70. 

—  and  movement,  46. 
Detonators,  187. 
Dichromate  of  ammonia,  183. 
Diffusion  of  gases,  195. 

—  influence  of  heaviness,  198. 

—  of  liquids,  194. 

—  in  mines,  198. 
Dilution,  general  action,  137. 

—  of  mine  air,  138. 
Distillation,  dry,  221. 
Door-ventilators,  60. 

EASE  of  "  catching  fire,"  173. 
Electric  flame,  179. 

—  lamps,  155. 

for  miners,  162. 

Electricity  and  its  sources,  209. 
Elements,  207. 
Expansion,  its  amount,  71. 

—  of  gases,  69. 

—  of  liquids,  73. 

—  of  solids,  68. 
Explosions,  generally,  128. 

—  in  closed  and  open  spaces,  129. 

—  in  mines,  138. 

—  petroleum  family,  n. 
Explosives,  185,  187,  188. 

FINENESS,  influence   on   ignition, 

Fire,  in  mines,  13,  175. 

—  its  extinction,  18,  19. 


Fire-damp,    composition    of,     107, 

122. 
Flame,  and  gauze,  92,  93. 

—  cooling  of,  88,  89. 

—  extinction  of,  85,  88. 

—  miner's  lamp,  148. 

—  shutting  up,  84. 

Flames,   bat's-wing  and   fish-tail, 

r  144- 

—  non-luminosity,  148. 

—  their  parts,  147. 

—  the  simplest,  147. 
Flash-point,  172. 

—  lamps,  155. 
Flue  gas,  217. 
Freezing-point  of  water,  75. 

GAS  and  flame,  differences,  146. 
Gas  mantles,  5. 
Gauze,  action  of,  95. 

—  experiments,  93. 

—  measurements,  94. 

Glass  tubing,  cutting  and  bending, 

49,  50. 

Glycerine,  184. 
Glycerine  nitrate,  184. 
Gob  fires,  176. 
Gunpowder,  185. 

—  speed  of  ignition,  185. 

HEAT,  action  on  petroleum,  etc. ,10. 

various  substances,  9. 

wires,  8. 

—  and  air,  6. 

chemical -change,  206. 

—  its  production,  157. 

—  increase  of  size  of  bodies,  67, 

68,  69. 

Holmes'  signal  light,  168. 
Hooke,  Robert,  5,  17,  21. 
Hydrogen,  its  explosive  force,  118. 

—  its  making,  117,  118. 
Hygrometer,  its  use,  28. 

—  pit,  40. 

loNixioN-point,  169. 

—  temperature,  167. 
Incandescent  gas  burner,  149. 
Inflammable  liquids,  131. 
Iron  and  sulphur,  202. 

Iron  sulphide,  117,  203. 


Index. 


229 


LAMPS,    Hailwood's    combustion, 
38. 

—  smothering  of,  19. 
Lavoisier,  Antoine,  18,  23,  25. 

MAGNESIUM,  its  combustion,  9. 
Mantle,  incandescent,  5. 

—  of  a  flame,  145. 

Marsh  gas,  explosive  amounts,  107. 

in  petroleum,  133. 

making  of,  109. 

origin  of,  no. 

properties  of,  109. 

Matches,  burning  in  carbon  dioxide, 
163. 

—  development  of,  159,  161. 

—  ease  ot  ignition,  170. 

—  explosive  part  of,  161. 
-   in  the  mine,  13,  140. 

—  making  of,  161. 
Measurement,  difficulties  of,  72. 
Mercury  oxide,  decomposition  of, 

24. 

Mine  air,  its  dilution,  138. 
Mines,  ventilation  of,  51. 
Miss-fired  shots,  190. 
Mixtures,  air  and  coal  gas,  135. 
marsh  gas,  107. 

—  iron  and  sulphur,  202. 

NEWTON,  Sir  Isaac,  201. 
Nitrate  of  ammonia,  183. 
—  copper,  180. 

glycerine    (nitro-glycerine), 

184. 

lead,  183. 

potash,  181. 

Nitric  acid,  181. 

OXIDES  of  nitrogen,  180. 
Oxygen,  activity  of,  206,  207. 

—  free  and  fixed,  23. 

—  percentages  for  no  burning,  26. 

—  products  in  combustion,  27. 

—  uses,  26. 

PARTICLES,  their  movements,  193. 

—  structure,  7. 

—  union,  205. 
Petrol  engines,  130. 

Petrol  explosive  mixtures,  130,. 


Petroleum,  crude,  132. 

—  discovery  of,  133. 

—  its  family,  132. 

—  solid  constituents,  132. 
Phosphorus",  and  air,  22. 

—  ignition  point,  169. 

—  in  carbon  disulphide,  168. 

—  red  and  yellow,  164. 
"  Pops,"  135. 

Pores  in  substances,  198. 
Pressure,  effect  on  vegetation,  219. 
Priestley,  Joseph,  23. 

REGULATORS,  61. 

Removal  of  gas  in  mines,  62. 

Rescue  apparatus,  41. 

Restlessness  of  particles,  193. 

Return  air,  composition  of,  121. 

Roaring  of  flames,  135. 

Room  ventilation,  53. 

Rust,  3,  200. 

Rusting,  a  form  of  combustion,  3. 

SAFETY  lamps,  varieties  of,  98. 

their  principle,  83. 

ventilation  of,  39. 

Scheele,  C.  W.,  23. 
Sheets,  hurdle,  123. 
—  ventilation,  59. 
Signal  lights,  168. 
Smoke,  212. 

Smoking  in  mines,  14,  140. 
Smuts,  213. 
Soot,  213. 
Sparks  of  electricity,  160. 

friction,  159. 

Splitting  of  air  current,  58. 
Spontaneous  ignition,  176. 

—  inflammability,  169. 
Stagnant  gas,  193. 
Stemming  a  shot,  188. 
Stink-damp,  detection,  116. 
making  of,  116. 

—  —  in  mines,  etc.,  117. 
Striking  back  of  flame,  134,  135. 
Surface  cooling,  95. 

TEMPERATURE,  and  colour,  8. 
—  sensation,  91. 

—  interesting  figures,  78. 

—  readings  which  coi  respond,  78. 


230  An  Introduction  to  Mining  Science. 


Temperature,  underground,  79. 
Test,  meaning  of  a,  30. 
Thermometer,  centigrade,  79. 

—  doubly  graduated,  76. 

—  in  mines,  80. 

—  principle  of,  74. 

—  range  of  graduation,  78. 

—  starting-points,  74,  75. 
Tobin's  tube,  53. 
Transformation  of  substances,  208. 

VENTILATION,  doors,  60. 

—  fans,  56. 

—  headings,  62. 


Ventilation,  sheets,  60. 

—  workings,  57,  58,  62. 

WATER,  its  boiling-point,  77. 

—  its  freezing-point,  75. 

—  its  vapour  in  air,  28,  29. 

—  propeities  of  its  vapour,  19. 
White-damp,  in,  125.         i    j 
Wood,  its  composition,  223. 

—  comparison  with  peat  and  coal, 

223. 

—  gas  compared   with    coal   gas, 


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